remove sqlserver 7 and 2000 support

[SimonCropp]

SQL Server 2000's mainstream support ended on April 8, 2008, and extended support ended on April 9, 2013. So it's been fully unsupported for over 12 years now.

[Copilot]

Pull request overview

This PR aims to remove legacy SQL Server 7.0 / 2000 compatibility paths (and related “Type System Version” handling) from SqlClient and its test TDS tooling.

Changes:

• Removed SQL Server 7.0 / 2000 mappings from the test TDS version helper and tightened supported TDS range to 2005–2012.
• Removed TypeSystemVersion=SQL Server 2000 parsing support and deleted SQL Server 2000-specific branches in SqlDataReader.
• Cleaned up several legacy-version comments across core TDS/transaction code paths.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/tests/tools/TDS/TDS/TDSVersion.cs	Removes SQL7/2000 version constants and mapping; tightens supported TDS range.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParser.cs	Updates legacy-version comments in TDS parsing logic.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsEnums.cs	Removes 2000-era versioning comment lines; updates datatype “version introduced” comment.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlParameter.cs	Simplifies legacy server notes around parameter size/type elevation.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlInternalTransaction.cs	Removes SQL7/2000-specific commentary from zombie handling explanation.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlDataReader.cs	Removes SQL Server 2000-specific type-system behavior and helper method.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlConnectionString.cs	Drops SQL Server 2000 from TypeSystemVersion recognized values.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Connection/SqlConnectionInternal.cs	Updates transaction enlistment comments to remove SQL7/2000 references.

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/tests/tools/TDS/TDS/TDSVersion.cs:53

• GetTDSVersion now throws NotSupportedException for server build majors other than 9/10/11. The simulated TDS server is still used in unit tests with ServerVersion majors 7 and 8 (e.g., tests/UnitTests/SimulatedServerTests/ConnectionTests.cs), so this will throw during server login handling and likely break those tests (and the ability to simulate legacy servers). Consider keeping mappings for 7.0/2000 in the test server, or update/remove the tests and any callers that still pass 7/8 versions.

            else
            {
                // Not supported TDS version
                throw new NotSupportedException("Specified build version is not supported");
            }

[Copilot]

IsSupported now requires tdsVersion >= SqlServer2005. For the simulated TDS server, this changes behavior when emulating SQL 7.0/2000: after resolving client/server versions, CheckTDSVersion will reject these versions and return an 'Unsupported TDS client version' error, instead of continuing far enough for the client to perform its own legacy-server rejection logic. If the intent is only to drop client support (not break simulation), keep legacy versions supported in the test server; otherwise, update/remove the tests and any code paths that rely on simulating these legacy versions.

Suggested change

	return tdsVersion >= SqlServer2005 && tdsVersion <= SqlServer2012;
	return tdsVersion <= SqlServer2012;

[Copilot]

The comment above SQLINT8/SQLVARIANT now says these datatypes are 'specific to 2005 (version 9) or later', but the file also treats some 7.0-era semantics separately (e.g., SQL70_DEFAULT_NUMERIC_PRECISION) and historically these tokens predate 2005. If the intent is to document when each token was introduced, consider splitting this into accurate groups (e.g., SQL 2000+/TDS 7.1+ vs SQL 2005+/TDS 7.2+), so future protocol work isn’t misled about type availability/version gates.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/tests/tools/TDS/TDS/TDSVersion.cs:53

• GetTDSVersion no longer handles server build versions with major 7 or 8. The simulated TDS server (GenericTdsServer.OnLogin7Request) calls TDSVersion.GetTDSVersion(Arguments.ServerVersion) during login, so starting a test server with ServerVersion = new Version(7, …) or new Version(8, …) will now result in an unhandled NotSupportedException instead of the server returning a clean “unsupported TDS version” response. This is likely to break existing simulated-server unit tests that validate the client rejects SQL Server 7.0/2000. Consider either keeping the 7.0/2000 mapping here for negative-testing purposes, or catching NotSupportedException at the call site and treating it as an unsupported version via CheckTDSVersion.

        public static Version GetTDSVersion(Version buildVersion)
        {
            // Check build version Major part
            if (buildVersion.Major == 11)
            {
                return SqlServer2012;
            }
            else if (buildVersion.Major == 10)
            {
                return SqlServer2008;
            }
            else if (buildVersion.Major == 9)
            {
                return SqlServer2005;
            }
            else
            {
                // Not supported TDS version
                throw new NotSupportedException("Specified build version is not supported");
            }