LibJS: Add missing steps and spec comments to PerformEval

While adding spec comments to PerformEval, I noticed we were missing
multiple steps.

Namely, these were:
- Checking if the host will allow us to compile the string
  (allowing LibWeb to perform CSP for eval)
- The parser's initial state depending on the environment around us
  on direct eval:
   - Allowing new.target via eval in functions
   - Allowing super calls and super properties via eval in classes
   - Disallowing the use of the arguments object in class field
     initializers at eval's parse time
- Setting ScriptOrModule of eval's execution context

The spec allows us to apply the additional parsing steps in any order.
The method I have gone with is passing in a struct to the parser's
constructor, which overrides the parser's initial state to (dis)allow
the things stated above from the get-go.

Userland/Libraries/LibJS/Runtime/VM.h

@@ -234,6 +234,7 @@ public:
     Function<void(Function<ThrowCompletionOr<Value>()>, Realm*)> host_enqueue_promise_job;
     Function<JobCallback(FunctionObject&)> host_make_job_callback;
     Function<ThrowCompletionOr<HostResizeArrayBufferResult>(GlobalObject&, size_t)> host_resize_array_buffer;
+    Function<ThrowCompletionOr<void>(Realm&, Realm&)> host_ensure_can_compile_strings;
 
 private:
     explicit VM(OwnPtr<CustomData>);