JS 'let' and 'const' error out in inline components

import QtQuick 2.15

Item {
  component Test: QtObject {
    function a() { var v = 1; console.log(v) } // works as expected
    function b() { let v = 1; console.log(v) } // Identifier v has already been declared
    function c() { const v = 1; console.log(v) } // Identifier v has already been declared
  }

  Test {id: t}

  Component.onCompleted: { 
    t.a(); t.b(); t.c()
  }
}