checkJs: allow file extensions other than .js

First of all, this option is super exciting! Thank you so much for the TypeScript team to make such an incredible tool ❤️

Surprisingly enough, this week I wanted to have type check in a *.jsfl file (Scripting for Adobe Animate) and it worked pretty well using Facebook's Flow. They have an option to configure a different file format other than .js.

It would be nice to allow this sort of configuration for TypeScript as well. I've naively tried to use "include":["./src/*.jsfl"] but it didn't worked. 😅

Or is there a hidden option for this? Thanks!

まず、checkJs と include パターンがサポートされているファイル拡張子をどのように扱うかを追跡し、報告された *.jsfl のケースを入口として使います。関連するコンパイラの動作とテストを特定し、その後、設定された .js 以外の拡張子が含められ、型チェックされることを、既存の JavaScript の動作を変更せずに確認します。