Add intrinsic analysis support for Type.GetMethod overload with genericParameterCount and BindingFlags

[Copilot]

This PR adds missing intrinsic analysis support for the new Type.GetMethod(string name, int genericParameterCount, BindingFlags bindingAttr, Type[] types) overload that was added in #94889.

Problem

The new overload was not properly handled by ILLink/ILC/ILLink.RoslynAnalyzer's intrinsic analysis. The current IntrinsicId.Type_GetMethod handling didn't account for the genericParameterCount parameter, causing the analysis to mark all methods with the given name regardless of their generic parameter count, rather than filtering by the specified count as the runtime does.

Solution

Enhanced the HandleCallAction.cs intrinsic handling to:

1. Detect genericParameterCount parameter: Added logic to identify when GetMethod overloads include an int genericParameterCount parameter at index 2
2. Extract genericParameterCount value: Added GetGenericParameterCountFromValue helper method to extract the parameter count from the argument values
3. Filter by generic parameter count: Created new ProcessGetMethodByName overload that filters methods by their generic parameter count using GetGenericParameters().Length
4. Handle all overload combinations: Supports both GetMethod(string, int, Type[]) and GetMethod(string, int, BindingFlags, Type[]) patterns

Testing

Added comprehensive test case GetMethod_Name_GenericParameterCount_BindingAttr_Types in MethodUsedViaReflection.cs to verify the analysis correctly marks only methods matching the specified generic parameter count.

The implementation ensures trimmer analysis behavior matches runtime behavior where:

// Only finds methods with exactly 1 generic parameter
var method = type.GetMethod("MyMethod", 1, BindingFlags.Public, new Type[] { typeof(int) });

Fixes #94989.

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[teo-tsirpanis]

The test seems wrong; the OnlyCalledViaReflection methods must be generic because the integer and Type[] parameters in Type.GetMethod refer to generic parameters.