Revert "[interp] Rework the allocation of offsets for variables (dotn…

…et#49072)"

This reverts commit 686f752.

Reverting this for now, as a workaround to get the AOT library tests
working again.

Running library tests with AOT+EnableAggressiveTrimming broke with:

```
  info: Arguments: --run,WasmTestRunner.dll,System.Buffers.Tests.dll,-notrait,category=OuterLoop,-notrait,category=failing
  info: Initializing.....
  fail: System.AggregateException: AggregateException_ctor_DefaultMessage (Arg_NullReferenceException)
         ---> System.NullReferenceException: Arg_NullReferenceException
           at Xunit.Sdk.ReflectionAttributeInfo.GetNamedArgument[Int32](String argumentName)
        --- End of stack trace from previous location ---
           at Xunit.Sdk.ReflectionAttributeInfo.GetNamedArgument[Int32](String argumentName)
        --- End of stack trace from previous location ---
           at Xunit.Sdk.ReflectionAttributeInfo.GetNamedArgument[Int32](String argumentName)
           Exception_EndOfInnerExceptionStack
  info: Discovering: System.Buffers.Tests.dll (method display = ClassAndMethod, method display options = None)
  info: WASM EXIT 1
  fail: Application has finished with exit code TESTS_FAILED but 0 was expected
```

More info: dotnet#49770

src/mono/mono/mini/interp/interp-internals.h

@@ -125,7 +125,10 @@ struct InterpMethod {
 	MonoType **param_types;
 	MonoJitInfo *jinfo;
 
-	guint32 locals_size;
+	// This doesn't include the size of stack locals
+	guint32 total_locals_size;
+	// The size of locals that map to the execution stack
+	guint32 stack_size;
 	guint32 alloca_size;
 	int num_clauses; // clauses
 	int transformed; // boolean