LibJS: Update parser to detect if identifier refer a "local" variable

This modification enables the parser to determine whether an identifier
used within a function refers to a local variable or not. In this
context, a local identifier means that it is not captured by any nested
function declaration which means it modified only from inside a
function.

The information about whether identifier is local is stored inside
Identifier AST node and also contains information about the index of
local variable inside a function and information about total number
of local variables used by a function is stored in function nodes.

Userland/Libraries/LibJS/Parser.h

@@ -342,6 +342,8 @@ private:
         }
     };
 
+    NonnullRefPtr<Identifier const> create_identifier_and_register_in_current_scope(SourceRange range, DeprecatedFlyString string);
+
     NonnullRefPtr<SourceCode const> m_source_code;
     Vector<Position> m_rule_starts;
     ParserState m_state;