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/javascriptreact.vim

@@ -4,4 +4,4 @@
 " Last Change:	2020 Aug 19
 
 " Placeholder for backwards compatilibity: .jsx used to stand for JavaScript.
-runtime! ftplugin/javascript.vim
+runtime! ftplugin/javascript[.]{vim,lua}