Add SuppressSourceLocation to BaseTestAttribute for library-declared tests

[Copilot]

Library-shipped test classes (used via [InheritsTests]) embed the library author's local file paths into test metadata via [CallerFilePath]. These paths are meaningless to consumers and pollute the binary.

Changes

• BaseTestAttribute: Added bool SuppressSourceLocation property (default false)
• Source generator (TestMetadataGenerator): Both GetTestMethodSourceLocation overloads return empty location when the property is set via named argument
• Reflection engine (ReflectionTestDataCollector): ExtractFilePath/ExtractLineNumber return empty/0 when suppressed
• Public API snapshots: Updated all Core verified files

Usage

public abstract class MyLibraryTests
{
    [Test(SuppressSourceLocation = true)]
    public void LibraryDefinedTest() { }
}

Consumers inheriting this test will see no source location rather than a path to a file on the library author's machine.

• Fixes [Feature]: Library-declared tests should not have their caller file location exposed #6220