fix(ftplugin): source inherited Lua ftplugins

Problem:
Vimscript ftplugins that inherit a base ftplugin often use explicit
`runtime! ftplugin/foo.vim` patterns. This skips corresponding Lua
ftplugins, unlike top-level ftplugin loading.

Solution:
Use the existing `{vim,lua}` patterns for bang runtime imports while
preserving each call's current lookup breadth.

runtime/ftplugin/bash.vim

@@ -15,6 +15,6 @@ unlet! b:is_sh
 unlet! b:is_kornshell
 let b:is_bash = 1
 
-runtime! ftplugin/sh.vim ftplugin/sh_*.vim ftplugin/sh/*.vim
+runtime! ftplugin/sh[.]{vim,lua} ftplugin/sh_*.{vim,lua} ftplugin/sh/*.{vim,lua}
 
 " vim: ts=8