[wasm] Improve locals visualization (#18919)

[wasm] Improve locals visualization (#18919)

* [wasm] Improve locals visualization in the debugger

- improves handling of generic types, null objects, delegates
- improves getting the name for nested types, arrays, generic types

top todos from this:
- Remove arity in "foo`2<int, int>" from the type name
- Convert nested type names from `foo/bar` to `foo.bar`.

* [wasm] Fix scoping for `mono_wasm_add_null_var`

- which caused runtime uncaught exceptions

* [wasm] Fix possible lost exception in GetScopeProperties

- An exception, eg., because of an invalid scope id just ends up
uncaught instead of showing up as a failed Result.

* [wasm] Address review feedback

- Replace `stringify_type` with `mono_type_full_name` which does exactly
the same thing!

* [wasm][debugger] Fixup nested class, and generic type names

```
	// Fix up generic names like Foo`2<int, string> to Foo<int, string>
	// and nested class names like Foo/Bar to Foo.Bar
```