Fix some native parameter two-pass rewriting in 'cswinrtgen'

[Sergio0694]

Title. This fixes two issues:

• Bad IL when unpinning string and Type parameters
• Incorrect call to Dispose for unmanaged value types

[Copilot]

Pull request overview

Fixes native parameter two-pass rewriting in cswinrtgen to avoid invalid IL for string/Type unpinning and to stop emitting disposal for unmanaged value-type ABI values.

Changes:

• Split value-type handling into managed vs unmanaged to avoid calling Dispose on unmanaged ABI value types.
• Emit a dedicated try/finally region for string and Type pin/unpin so unpinning doesn’t end up after a leave.s within another protected region.
• Minor documentation/comment additions around the new flow.

Comments suppressed due to low confidence (2)

src/WinRT.Interop.Generator/Rewriters/InteropMethodRewriter.NativeParameter.cs:292

• The newly added method parameter is not used inside RewriteBodyForTypeOfString. Consider removing it (and the corresponding argument at the call site) to keep the helper signature minimal, unless you plan to use it for validation/debug output.

            CilMethodBody body,
            CilInstruction tryMarker,
            CilInstruction loadMarker,
            CilInstruction finallyMarker,
            int parameterIndex,
            InteropReferences interopReferences,

src/WinRT.Interop.Generator/Rewriters/InteropMethodRewriter.NativeParameter.cs:391

• The newly added method parameter is not used inside RewriteBodyForTypeOfType. Consider removing it (and the corresponding argument at the call site) to reduce noise unless it will be used.

            CilInstruction loadMarker,
            CilInstruction finallyMarker,
            int parameterIndex,
            InteropReferences interopReferences,
            ModuleDefinition module)
        {
            // Declare the local variables:

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