LibJS: Let invokers (callers) of [[Call]] allocate ExecutionContext

Instead of letting every [[Call]] implementation allocate an
ExecutionContext, we now make that a responsibility of the caller.

The main point of this exercise is to allow the Call instruction
to write function arguments directly into the callee ExecutionContext
instead of copying them later.

This makes function calls significantly faster:
- 10-20% faster on micro-benchmarks (depending on argument count)
- 4% speedup on Kraken
- 2% speedup on Octane
- 5% speedup on JetStream

Libraries/LibWeb/WebDriver/ExecuteScript.cpp

@@ -92,7 +92,7 @@ static JS::ThrowCompletionOr<JS::Value> execute_a_function_body(HTML::BrowsingCo
     // 9. Let completion be Function.[[Call]](window, parameters) with function as the this value.
     // NOTE: This is not entirely clear, but I don't think they mean actually passing `function` as
     // the this value argument, but using it as the object [[Call]] is executed on.
-    auto completion = function->internal_call(window, parameters);
+    auto completion = JS::call(realm.vm(), *function, window, parameters);
 
     // 10. Clean up after running a callback with environment settings.
     HTML::clean_up_after_running_callback(realm);