RunFileTests: bring missing changes from 10.0.4xx

[jjonescz]

Some changes were missed during automatic flows, probably due to badly resolved merge conflicts.

[Copilot]

Pull request overview

Brings in missed test coverage changes from 10.0.4xx, primarily expanding validation around file-based program directives (notably #:ref), warning behavior, and some output assertion tightening.

Changes:

• Added extensive new tests for #:ref directive behavior (paths, errors, transitivity, cycles, feature flagging, and interactions with #:include).
• Added tests and adjusted assertions around dotnet run warning/no-warning scenarios and missing shebang warning (CA2266).
• Introduced a shared test helper to enable the experimental #:ref directive via Directory.Build.props.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/Run/RunFileTests_General.cs	Adds stdin #:ref test and expands dotnet run warning/no-warning coverage; tightens stdout/stderr assertions.
test/dotnet.Tests/CommandTests/Run/RunFileTests_Directives.cs	Adds comprehensive #:ref directive test suite; adjusts include-mapping test line numbers due to shebang insertion.
test/dotnet.Tests/CommandTests/Run/RunFileTests_CscOnlyAndApi.cs	Adds tests covering up-to-date / csc-only behavior with #:ref, VirtualProjectBuilder PRE lifetime regression tests, and a virtual PRE creation test.
test/dotnet.Tests/CommandTests/Run/RunFileTests_BuildOptions.cs	Adds missing-shebang CA2266 warning tests; removes some now-unneeded test setup noise.
test/dotnet.Tests/CommandTests/Run/RunFileTests_BuildCommands.cs	Removes trailing whitespace (no functional change).
test/dotnet.Tests/CommandTests/Run/RunFileTestBase.cs	Adds EnableRefDirective helper and binlog evaluation count helper support.
test/dotnet.Tests/CommandTests/Project/Convert/DotnetProjectConvertTests.cs	Adds conversion tests for #:ref (direct, transitive, collisions, item copy/delete, and conversion scoping).