C#: Fix numeric literal type attribution to reflect suffix

[knutwannheden]

Motivation

Numeric literals with type suffixes (e.g., 0L, 1.0F, 2.0D) were all attributed as JavaType.Primitive(Int) because GetPrimitiveType hardcoded NumericLiteralExpression to Int, ignoring the actual type. This forced downstream recipes like MarkLocalVariableAsConst (in recipes-csharp) to implement a workaround (InferTypeFromLiteralSuffix) that manually parsed suffixes from ValueSource — which itself had bugs (e.g., interpreting . in string literals as double).

Summary

• Use Roslyn's SemanticModel.GetTypeInfo() via _typeMapping?.Type(node) to resolve the correct type for numeric literals, falling back to the hardcoded Int only when no semantic model is available
• Add Parse() and FindFirst<T>() test helpers to RewriteTest for tests that need to inspect AST node properties beyond round-trip printing
• Add parameterized test covering 0L, 0l, 42, 1.0f, 1.0F, 1.0d, 1.0D, and 1.0 with their expected primitive kinds

Test plan

• All 8 new NumericLiteralTypeAttribution test cases pass
• All 15 LiteralTests pass (existing + new)
• Full C# test suite passes (1780 tests, 0 failures)