Adds C# IL extractor prototype (minimally scoped for now to detect methods/control flow) an some simple example queries to demonstrate it can detect method calls from compiled database.

---- Copilot Summary ---
Extractor Implementation:

• Added the initial extractor inSemmle.Extraction.CSharp.IL, includingILExtractor.cs for reading assemblies and writing facts,TrapWriter.cs for TRAP file output, andProgram.cs as the CLI entry point. The extractor captures assemblies, types, methods, IL instructions, control flow, calls, and exception handlers.[1][2][3]

Schema and Configuration:

• Defined the database schema for C# IL extraction insemmlecode.csharp.il.dbscheme, specifying tables for assemblies, types, methods, IL instructions, control flow, call targets, operands, and exception handlers.
• Added extractor and QL library configuration files:codeql-extractor.yml for extractor metadata,qlpack.yml for QL library, anddowngrades/qlpack.yml for downgrade support.[1][2][3]

Documentation and Project Structure:

• Created a comprehensiveREADME.md describing the extractor’s features, usage, schema, use cases, design philosophy, limitations, and directory layout.

Build and Environment:

• Added.gitignore for C# build artifacts and test results, and a.csproj file for the extractor project targeting .NET 8.0 and referencing Mono.Cecil.[1][2]