LibJS: Add an inline JIT fast path when ToNumeric has nothing to do

In most cases, this op will do nothing, as it is running on an the
accumulator while it already contains a number. Let's avoid doing that
native call.

Userland/Libraries/LibJS/JIT/Compiler.h

@@ -166,6 +166,8 @@ private:
 
     void native_call(void* function_address, Vector<Assembler::Operand> const& stack_arguments = {});
 
+    void jump_if_int32(Assembler::Reg, Assembler::Label&);
+
     template<typename Codegen>
     void branch_if_int32(Assembler::Reg, Codegen);