Use Framework SourceType for WASM pass-through assets in multi-client solutions

When multiple Blazor WebAssembly client projects reference the same runtime pack,
pass-through files (JS, maps, ICU data, native wasm) share a NuGet cache path.
This causes duplicate Identity keys in the static web assets pipeline, crashing
DiscoverPrecompressedAssets with an ArgumentException.

Instead of copying pass-throughs to the intermediate output path (which risks staleness
on incremental builds when the runtime pack changes), materialize them to a per-project
obj/fx/{PackageId}/ directory using the Framework SourceType convention from the SWA SDK.
This gives each project a unique Identity while properly modeling the relationship:
these are framework assets adopted by each consuming project.

- Pass-through files: copied to obj/fx/{PackageId}/, registered with SourceType=Framework
- WebCil-converted files: remain in obj/webcil/, registered with SourceType=Computed
- Satellite assemblies: placed in culture subdirectories in both cases
- Both groups get per-item ContentRoot for correct Identity resolution

Requires SDK support for SourceType=Framework (dotnet/sdk#53135).

Fixes duplicate-key crash introduced by #124125.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lewing

src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets

@@ -353,23 +353,60 @@ Copyright (c) .NET Foundation. All rights reserved.
     <PropertyGroup>
       <_WasmBuildWebcilPath>$([MSBuild]::NormalizeDirectory($(IntermediateOutputPath), 'webcil'))</_WasmBuildWebcilPath>
       <_WasmBuildTmpWebcilPath>$([MSBuild]::NormalizeDirectory($(IntermediateOutputPath), 'tmp-webcil'))</_WasmBuildTmpWebcilPath>
+      <_WasmFrameworkAssetPath>$([MSBuild]::NormalizeDirectory($(IntermediateOutputPath), 'fx', '$(PackageId)'))</_WasmFrameworkAssetPath>
     </PropertyGroup>
 
     <ConvertDllsToWebcil Candidates="@(_BuildAssetsCandidates)" IntermediateOutputPath="$(_WasmBuildTmpWebcilPath)" OutputPath="$(_WasmBuildWebcilPath)" IsEnabled="$(_WasmEnableWebcil)">
       <Output TaskParameter="WebcilCandidates" ItemName="_WebcilAssetsCandidates" />
       <Output TaskParameter="FileWrites" ItemName="FileWrites" />
     </ConvertDllsToWebcil>
 
+    <!-- Materialize framework pass-through files (JS, maps, ICU, native wasm, and when WebCil is
+         disabled, DLLs) from shared locations (e.g. NuGet cache) to a per-project directory.
+         Webcil-converted files already live in per-project $(IntermediateOutputPath)webcil/ and
+         don't need materialization. Framework assets are copied to obj/fx/{PackageId}/ following
+         the SWA Framework SourceType convention so each project gets a unique Identity.
+         Satellite assemblies are placed in culture subdirectories to match ConvertDllsToWebcil. -->
     <ItemGroup>
+      <_WasmFrameworkCandidates Include="@(_WebcilAssetsCandidates)"
+        Condition="!$([System.String]::new('%(Identity)').StartsWith($(_WasmBuildWebcilPath)))" />
+      <_WebcilAssetsCandidates Remove="@(_WasmFrameworkCandidates)" />
+    </ItemGroup>
+
+    <!-- Separate satellite (culture) assets from regular ones so we can place them in subdirs -->
+    <ItemGroup>
+      <_WasmCultureFrameworkAssets Include="@(_WasmFrameworkCandidates)"
+        Condition="'%(_WasmFrameworkCandidates.AssetTraitName)' == 'Culture'" />
+      <_WasmFrameworkCandidates Remove="@(_WasmCultureFrameworkAssets)" />
+    </ItemGroup>
+
+    <Copy SourceFiles="@(_WasmFrameworkCandidates)"
+      DestinationFolder="$(_WasmFrameworkAssetPath)"
+      SkipUnchangedFiles="true" />
+
+    <Copy SourceFiles="@(_WasmCultureFrameworkAssets)"
+      DestinationFiles="@(_WasmCultureFrameworkAssets->'$(_WasmFrameworkAssetPath)%(AssetTraitValue)/%(Filename)%(Extension)')"
+      SkipUnchangedFiles="true"
+      Condition="'@(_WasmCultureFrameworkAssets)' != ''" />
+
+    <ItemGroup>
+      <FileWrites Include="@(_WasmFrameworkCandidates->'$(_WasmFrameworkAssetPath)%(Filename)%(Extension)')" />
+      <FileWrites Include="@(_WasmCultureFrameworkAssets->'$(_WasmFrameworkAssetPath)%(AssetTraitValue)/%(Filename)%(Extension)')" />
+      <_WasmMaterializedFrameworkAssets Include="@(_WasmFrameworkCandidates->'$(_WasmFrameworkAssetPath)%(Filename)%(Extension)')" />
+      <_WasmMaterializedFrameworkAssets Include="@(_WasmCultureFrameworkAssets->'$(_WasmFrameworkAssetPath)%(AssetTraitValue)/%(Filename)%(Extension)')" />
       <!-- Set per-item ContentRoot so each asset's Identity matches its actual file on disk -->
       <_WebcilAssetsCandidates Update="@(_WebcilAssetsCandidates)" ContentRoot="%(RootDir)%(Directory)" />
+      <_WasmMaterializedFrameworkAssets Update="@(_WasmMaterializedFrameworkAssets)" ContentRoot="%(RootDir)%(Directory)" />
       <_WasmFingerprintPatterns Include="WasmFiles" Pattern="*.wasm" Expression="#[.{fingerprint}]!" />
       <_WasmFingerprintPatterns Include="DllFiles" Pattern="*.dll" Expression="#[.{fingerprint}]!" />
       <_WasmFingerprintPatterns Include="DatFiles" Pattern="*.dat" Expression="#[.{fingerprint}]!" />
       <_WasmFingerprintPatterns Include="Pdb" Pattern="*.pdb" Expression="#[.{fingerprint}]!" />
       <_WasmFingerprintPatterns Include="Symbols" Pattern="*.js.symbols" Expression="#[.{fingerprint}]!" />
     </ItemGroup>
 
+    <!-- Webcil-converted assets are per-project (Computed); materialized framework assets
+         are adopted from the runtime pack (Framework). Define them separately so the SWA
+         pipeline can handle Framework materialization/ownership correctly. -->
     <DefineStaticWebAssets
       CandidateAssets="@(_WebcilAssetsCandidates)"
       SourceId="$(PackageId)"
@@ -385,6 +422,21 @@ Copyright (c) .NET Foundation. All rights reserved.
       <Output TaskParameter="Assets" ItemName="WasmStaticWebAsset" />
     </DefineStaticWebAssets>
 
+    <DefineStaticWebAssets
+      CandidateAssets="@(_WasmMaterializedFrameworkAssets)"
+      SourceId="$(PackageId)"
+      SourceType="Framework"
+      AssetKind="Build"
+      AssetRole="Primary"
+      CopyToOutputDirectory="PreserveNewest"
+      CopyToPublishDirectory="Never"
+      FingerprintCandidates="$(_WasmFingerprintAssets)"
+      FingerprintPatterns="@(FingerprintPatterns);@(_WasmFingerprintPatterns)"
+      BasePath="$(StaticWebAssetBasePath)"
+    >
+      <Output TaskParameter="Assets" ItemName="WasmStaticWebAsset" />
+    </DefineStaticWebAssets>
+
     <DefineStaticWebAssets
       CandidateAssets="@(_WasmDiscoveredFileCandidates)"
       AssetTraitName="WasmResource"