[Wasm] Ensure monovm_initialize is called on startup and address other startup items...

[Wasm] Ensure monovm_initialize is called on startup and address other startup items (#39446)

This PR addresses:

- Calling monovm_initialize matches how other mono platforms init themselves (Fixes https://github.com/dotnet/runtime/issues/39074)
- Set the entry assembly (Fixes https://github.com/dotnet/runtime/issues/38994)
- Make sure the assembly location is set to empty for assemblies that are loaded from memory (Fixes https://github.com/dotnet/runtime/issues/39650)