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/objc.vim

@@ -10,4 +10,4 @@ if exists("b:did_ftplugin")
 endif
 
 " Behaves just like C
-runtime! ftplugin/c.vim ftplugin/c_*.vim ftplugin/c/*.vim
+runtime! ftplugin/c[.]{vim,lua} ftplugin/c_*.{vim,lua} ftplugin/c/*.{vim,lua}