[mono][wasm] Fix ldftn in AOT mode, it should return a ftndesc. (#82282)

* [mono][wasm] Fix ldftn in AOT mode, it should return a ftndesc.

Fixes #82272.

* Reenable tests.

src/libraries/System.Reflection/tests/MethodInfoTests.cs

@@ -896,7 +896,6 @@ private static void SecondCall(MethodInfo mi)
 
         [Fact]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/71883", typeof(PlatformDetection), nameof(PlatformDetection.IsNativeAot))]        
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/82272", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser))]        
         private static unsafe void TestFunctionPointers()
         {
             void* fn = FunctionPointerMethods.GetFunctionPointer();

src/mono/mono/mini/jit-icalls.c

@@ -21,6 +21,7 @@
 #include "jit-icalls.h"
 #include "aot-runtime.h"
 #include "mini-runtime.h"
+#include "llvmonly-runtime.h"
 #include <mono/utils/mono-error-internals.h>
 #include <mono/metadata/exception-internals.h>
 #include <mono/metadata/threads-types.h>
@@ -42,17 +43,19 @@ mono_ldftn (MonoMethod *method)
 
 	if (mono_llvm_only) {
 		// FIXME: No error handling
+		if (mono_method_signature_internal (method)->pinvoke) {
+			addr = mono_compile_method_checked (method, error);
+			mono_error_assert_ok (error);
+			g_assert (addr);
 
-		addr = mono_compile_method_checked (method, error);
-		mono_error_assert_ok (error);
-		g_assert (addr);
-
-		if (mono_method_needs_static_rgctx_invoke (method, FALSE))
-			/* The caller doesn't pass it */
-			g_assert_not_reached ();
+			return addr;
+		} else {
+			/* Managed function pointers are ftndesc's */
+			addr = mini_llvmonly_load_method_ftndesc (method, FALSE, FALSE, error);
+			mono_error_assert_ok (error);
 
-		addr = mini_add_method_trampoline (method, addr, mono_method_needs_static_rgctx_invoke (method, FALSE), FALSE);
-		return addr;
+			return addr;
+		}
 	}
 
 	/* if we need the address of a native-to-managed wrapper, just compile it now, trampoline needs thread local