Add C#14 extension members

[PhenX]

Fixes #141

[Copilot]

Pull request overview

This pull request adds support for C# 14 extension members to the EntityFrameworkCore.Projectables source generator. Extension members are a new C# 14 feature that allow defining members within an extension() block, providing a more natural syntax for extending types compared to traditional extension methods.

Changes:

• Updated Microsoft.CodeAnalysis.CSharp to version 5.0.0 to support C# 14 features
• Modified the source generator to detect and process extension members using the IsExtension property
• Added logic to rewrite extension parameter references (e.g., e) to @this in generated expressions
• Added comprehensive test coverage including generator tests and functional tests for extension member properties, methods, and methods with parameters

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Directory.Packages.props	Updated Microsoft.CodeAnalysis.CSharp from 4.11.0 to 5.0.0
Directory.Build.props	Added conditional LangVersion 14.0 for net10.0 target framework
ProjectableInterpreter.cs	Added extension member detection and handling logic with helper methods
ExpressionSyntaxRewriter.cs	Added extension parameter name tracking and identifier replacement
ProjectionExpressionGeneratorTests.cs	Added 5 generator tests for extension member scenarios (NET10_0_OR_GREATER)
ExtensionMemberTests.cs	Added 2 functional tests for extension member methods
EntityExtensions.cs	Added extension member definitions for Entity and int types
Entity.cs	Added Entity class for extension member testing
Various .verified.txt files	Expected output verification files for all new tests

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