File-based apps: ensure shebang analyzer only applies to #:include

[jjonescz]

To avoid breaking people that include .cs files via other means. See #53749 (comment).

[Copilot]

Pull request overview

This PR narrows the CA2266 (“missing shebang in file-based program”) behavior so it only triggers when additional C# source files are brought in via #:include, avoiding warnings for multi-file compilations caused by other MSBuild mechanisms (e.g., Directory.Build.props, project references, etc.).

Changes:

• Emit compiler-visible item metadata in the generated virtual project so analyzers can distinguish #:include-added Compile items.
• Update the CA2266 analyzer logic to only warn when a non-entrypoint syntax tree is marked as coming from #:include.
• Adjust/extend CLI and analyzer unit tests to validate the new behavior and the generated project content.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/Run/RunFileTests_Directives.cs	Updates API-based virtual project assertions to require the new compiler-visible metadata declaration.
test/dotnet.Tests/CommandTests/Run/RunFileTests_CscOnlyAndApi.cs	Updates expected virtual project XML in CscOnly/API tests to include the compiler-visible metadata item.
test/dotnet.Tests/CommandTests/Run/RunFileTests_BuildOptions.cs	Updates CA2266 expectations to ensure no warning from extra Compile items added via Directory.Build.props, while still warning for real #:include.
src/Microsoft.DotNet.ProjectTools/VirtualProjectBuilder.cs	Adds <CompilerVisibleItemMetadata ...> so FileBasedProgramsFromIncludeDirective flows into analyzer config as build_metadata.Compile.*.
src/Microsoft.CodeAnalysis.NetAnalyzers/tests/.../MissingShebangInFileBasedProgramTests.cs	Updates/extends analyzer tests to cover “include vs non-include extra file” behavior.
src/Microsoft.CodeAnalysis.NetAnalyzers/src/.../CSharpMissingShebangInFileBasedProgram.cs	Changes CA2266 triggering condition to require presence of build_metadata.Compile.FileBasedProgramsFromIncludeDirective=true on at least one non-entrypoint tree.