ts: integrate ts-*-mode-install into each language mode (perl.l, c-mode.l, etc.)

[snmsts]

Currently users must call ts-c-mode-install / ts-perl-mode-install etc. explicitly from ~/.xyzzy.

Goal

Move the ts setup into each language mode's own .l file, so tree-sitter highlighting and indentation activate automatically when the grammar DLL is present — without any user-side install calls.

Benefit

• Restores correct autoload semantics (perl.l only loaded when a .pl file is opened)
• No manual setup required once grammar DLLs are bundled