Add regression tests for generic type parameter reflection properties

[Copilot]

Summary

Adds regression tests to verify the correct behavior of reflection properties for generic type parameters (e.g., T from List<T>), specifically addressing the scenario described in the issue where processing unbound generic types like typeof(List<>) through reflection can lead to StackOverflowException.

Root Cause Analysis

The reported StackOverflowException is not a runtime bug. It is caused by user code that recursively walks both Type.DeclaringType and Type.GetGenericArguments() without checking Type.IsGenericParameter, creating an infinite cycle:

1. typeof(List<>).GetGenericArguments() returns [T] (the type parameter)
2. T.DeclaringType returns typeof(List<>) (the declaring generic type definition)
3. Processing typeof(List<>) again leads back to step 1 → infinite recursion

This circular reference between DeclaringType and GetGenericArguments() is by design. The correct pattern is to check type.IsGenericParameter before recursing through DeclaringType, as demonstrated in the runtime's own TypeNameBuilder.cs:

for (Type? t = rootType; t != null; t = t.IsGenericParameter ? null : t.DeclaringType)

Changes

Added two test methods to TypeTests.cs:

• GenericTypeParameter_Properties (Theory with 6 cases): Verifies that generic type parameters correctly report IsGenericType=false, IsGenericParameter=true, FullName=null, expected Name, and correct DeclaringType for parameters from List<>, Dictionary<,>, Outside<>, and Outside<>.Inside<>.

• GenericTypeDefinition_GetGenericArguments_DeclaringTypeCycle: Documents and verifies the by-design circular reference between DeclaringType and GetGenericArguments() for both single-parameter (List<>) and multi-parameter (Dictionary<,>) generic type definitions.

Test Results

All 7 new tests pass. Full test suite (68,089 tests) passes with 0 failures.