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 ..."

Final の仕様の構文セクションから始め、仕様と関連ドキュメントを調べて、Final と Final[X] の既存の説明を探します。完了とは、2 つの形式について、「ベア」や「明示的に型付けされた」などの用語を使った、明確で一貫して命名された定義があり、他の箇所に矛盾する表現が残っていない状態です。