LibJS: Move [[ThisMode]] to ECMAScriptFunctionObject

Author: https://github.com/linusg
Commit: 1e97a85095
Pull-request: https://github.com/SerenityOS/serenity/pull/10203
Reviewed-by: https://github.com/IdanHo ✅
Reviewed-by: https://github.com/davidot

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -51,11 +51,11 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(GlobalObject& global_object,
 {
     // NOTE: This logic is from OrdinaryFunctionCreate, https://tc39.es/ecma262/#sec-ordinaryfunctioncreate
     if (m_is_arrow_function)
-        set_this_mode(ThisMode::Lexical);
+        m_this_mode = ThisMode::Lexical;
     else if (m_strict)
-        set_this_mode(ThisMode::Strict);
+        m_this_mode = ThisMode::Strict;
     else
-        set_this_mode(ThisMode::Global);
+        m_this_mode = ThisMode::Global;
 
     // 15.1.3 Static Semantics: IsSimpleParameterList, https://tc39.es/ecma262/#sec-static-semantics-issimpleparameterlist
     set_has_simple_parameter_list(all_of(m_formal_parameters, [&](auto& parameter) {