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/Parser.h

@@ -43,7 +43,14 @@ class ScopePusher;
 
 class Parser {
 public:
-    explicit Parser(Lexer lexer, Program::Type program_type = Program::Type::Script);
+    struct EvalInitialState {
+        bool in_eval_function_context { false };
+        bool allow_super_property_lookup { false };
+        bool allow_super_constructor_call { false };
+        bool in_class_field_initializer { false };
+    };
+
+    explicit Parser(Lexer lexer, Program::Type program_type = Program::Type::Script, Optional<EvalInitialState> initial_state_for_eval = {});
 
     NonnullRefPtr<Program> parse_program(bool starts_in_strict_mode = false);
 
@@ -300,6 +307,7 @@ private:
         bool allow_super_property_lookup { false };
         bool allow_super_constructor_call { false };
         bool in_function_context { false };
+        bool in_eval_function_context { false }; // This controls if we allow new.target or not. Note that eval("return") is not allowed, so we have to have a separate state variable for eval.
         bool in_formal_parameter_context { false };
         bool in_generator_function_context { false };
         bool await_expression_is_valid { false };