LibJS: Split parsing program to script and module separately

This allows us to only perform checks like export bindings existing only
for modules. Also this makes it easier to set strict and other state
variables with TemporaryChanges.

Userland/Libraries/LibJS/Parser.h

@@ -176,6 +176,9 @@ public:
 private:
     friend class ScopePusher;
 
+    void parse_script(Program& program, bool starts_in_strict_mode);
+    void parse_module(Program& program);
+
     Associativity operator_associativity(TokenType) const;
     bool match_expression() const;
     bool match_unary_prefixed_expression() const;