Spec: `Final` section could use better definition for `Final` vs. `Final[X]`

Came up in #2353: Currently, the syntax section for Final uses the following definitions:

Final may be used in one of several forms:

• With an explicit type, using the syntax Final[<type>] [...]
• With no type annotation. [...]

As @carljm points out, these definitions are not great. I suggest to give them better names and use those consistently in the spec (and elsewhere). Carl used "bare" for the latter case, which I like. Maybe "explicitly typed" for the former? "When using a bare Final ..." or "When using an explicitly typed Final ..."

从规范中关于 Final 的语法部分开始，并在规范及相关文档中查找对 Final 和 Final[X] 的现有描述。完成的标准是：这两种形式都有清晰且命名一致的定义，使用“裸”和“显式类型化”等术语，并且其他地方不再残留相互冲突的措辞。