Extract TypeMention for catch (Exception) clauses

[Copilot]

Specific C# catch clauses are already distinguished from general catch {} clauses via catch_type, but catch (Exception) did not extract the exception type as a TypeMention unless a variable was also declared. This change makes catch (Exception) extract its TypeMention directly under the catch clause, aligning it with the typed catch shape already exposed for catch (Exception e).

• Extractor behavior

  • Emit a TypeMention from Catch when the clause is of the form catch (T) and has no variable declaration.
  • Keep existing behavior unchanged for:
    • catch {} → general catch, no type mention
    • catch (T e) → specific catch, type mention remains attached via the variable declaration

• AST shape

  • catch (T) now contributes:
    • catch_type(..., T, specific)
    • TypeMention(T) as a direct child of the catch clause
  • This gives the QL side a consistent typed representation for both forms of specific catch clauses.

• Regression coverage

  • Extend the C# type-mention regression corpus with a catch (Exception) example.
  • Update the expected output to include the extracted Exception type mention.

try
{
}
catch (Exception)
{
}

Expected extractor effect: Exception is now present as a TypeMention child of the catch clause.

[Copilot]

Pull request overview

This PR updates the C# extractor to emit a TypeMention directly under a Catch clause for typed catch clauses without a variable declaration (e.g., catch (Exception)), aligning the AST shape with existing typed catches that declare a variable (e.g., catch (Exception e)).

Changes:

• Update Catch extraction to create a TypeMention for catch (T) clauses that omit a variable identifier.
• Extend the type-mention regression test corpus to include catch (Exception) and update expected results.
• Update PrintAst expectations to reflect the new TypeMention child under SpecificCatchClause for catch (T) without a variable.

Show a summary per file

File	Description
csharp/extractor/Semmle.Extraction.CSharp/Entities/Statements/Catch.cs	Emits a TypeMention under the catch clause for catch (T) with no variable.
csharp/ql/test/library-tests/regressions/Program.cs	Adds a catch (Exception) example to exercise the new extraction behavior.
csharp/ql/test/library-tests/regressions/TypeMentions.expected	Updates expected TypeMention results to include the new void return type and Exception in catch (Exception).
csharp/ql/test/library-tests/csharp6/PrintAst.expected	Updates AST print expectations so catch (T) now has a TypeMention child.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0