Implement global MSBuild defaults for [Projectable] options

[koenbeuk]

Introduce global MSBuild defaults for [Projectable] options, enhancing attribute handling and allowing for project-wide configuration. This change enables the use of global settings while maintaining the ability to override them at the member level.

closes #133

[Copilot]

Pull request overview

Adds support for project-wide defaults for [Projectable] options by flowing MSBuild global properties (CompilerVisibleProperty → build_property.*) into the generator and applying them as fallbacks when the attribute doesn’t specify an option.

Changes:

• Introduces ProjectableGlobalOptions and wires global analyzer config options into the incremental generator pipeline.
• Updates attribute snapshotting to preserve “unset vs explicitly set” semantics (nullable option fields) so member-level settings can override global defaults.
• Adds generator tests that inject MSBuild global properties via AnalyzerConfigOptionsProvider.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/EntityFrameworkCore.Projectables.Generator.Tests/ProjectionExpressionGeneratorTestsBase.cs	Adds a new RunGenerator overload and helper types to inject MSBuild global properties in generator tests.
tests/EntityFrameworkCore.Projectables.Generator.Tests/GlobalOptionsTests.cs	New tests validating global defaults and member-level overrides for key [Projectable] options.
src/EntityFrameworkCore.Projectables.Generator/ProjectionExpressionGenerator.cs	Plumbs global options into the generator pipeline and execution path.
src/EntityFrameworkCore.Projectables.Generator/Models/ProjectableGlobalOptions.cs	New model that snapshots build_property.Projectables_* values from global analyzer config options.
src/EntityFrameworkCore.Projectables.Generator/Models/ProjectableAttributeData.cs	Changes option fields to nullable so absence can fall back to global defaults.
src/EntityFrameworkCore.Projectables.Generator/Interpretation/ProjectableInterpreter.cs	Resolves effective option values with precedence: attribute → global MSBuild default → hard-coded fallback.
src/EntityFrameworkCore.Projectables.Generator/Comparers/MemberDeclarationSyntaxAndCompilationEqualityComparer.cs	Includes global options in incremental equality/hashing so changes invalidate cached results correctly.
src/EntityFrameworkCore.Projectables.Abstractions/build/EntityFrameworkCore.Projectables.Abstractions.props	Adds CompilerVisibleProperty declarations (and placeholder properties) to expose MSBuild values to the compiler/generator.
src/EntityFrameworkCore.Projectables.Abstractions/EntityFrameworkCore.Projectables.Abstractions.csproj	Packs the new .props file into the NuGet package.

[Copilot]

Projectables_NullConditionalRewriteSupport is parsed with Enum.TryParse, which will also accept numeric values (and potentially undefined enum values) as valid. That means a malformed MSBuild value like 999 would silently become an effective option rather than being treated as "not set". Consider validating with Enum.IsDefined (or rejecting numeric-only inputs) so malformed values are ignored consistently with the bool options tests.

Suggested change

	&& Enum.TryParse<NullConditionalRewriteSupport>(nullConditionalStr, ignoreCase: true, out var nullConditional))
	&& Enum.TryParse<NullConditionalRewriteSupport>(nullConditionalStr, ignoreCase: true, out var nullConditional)
	&& Enum.IsDefined(typeof(NullConditionalRewriteSupport), nullConditional))