Separate tree-sitter and non-tree-sitter variant of sh-mode

Separate tree-sitter and non-tree-sitter variant of sh-mode

Now there are three modes, sh-base-mode, sh-mode, bash-ts-mode.

The change I made: change sh-mode to sh-base-mode, remove docstring.
Below the new sh-base-mode, create a new definition for sh-mode, paste
the dostring, add setup for font-lock-defaults.  Below sh-mode, add
bash-ts-mode.

* lisp/progmodes/sh-script.el (sh-mode): Moves all setup into
sh-base-mode, except for the setup for font-lock-defaults and the
docstring.
(sh-base-mode): New mode.
(bash-ts-mode): New mode.