Fix #12074: Preserve container when opening View Page Source

When 'View Page Source' is triggered from a container tab, the view-source
tab now inherits the userContextId from the originating tab. This ensures
that the source view maintains the same authentication/session context as
the original page.

The fix checks if a view-source URL is being opened without an explicit
userContextId parameter and automatically inherits it from the currently
selected tab before processing through Zen's workspace/container logic.

Author: R0h1tAnand

src/browser/components/tabbrowser/content/tabbrowser-js.patch

@@ -266,6 +266,17 @@ index 0eaca7a58e0026237b71b2ad515efe84d9e8c779..2ab8633d0378e5a25cf75c50b29d4689
          );
        }
 
++      if (
++        userContextId === undefined &&
++        aURI?.spec?.startsWith("view-source:") &&
++        this.selectedTab
++      ) {
++        const selectedUserContextId = this.selectedTab.getAttribute("usercontextid");
++        if (selectedUserContextId) {
++          userContextId = parseInt(selectedUserContextId, 10);
++        }
++      }
++
 +      let hasZenDefaultUserContextId = false;
 +      let zenForcedWorkspaceId = undefined;
 +      if (typeof gZenWorkspaces !== "undefined" && !_forZenEmptyTab) {