Undo ftplugin and indent settings when filetype changes

Set b:undo_ftplugin for matchpairs, matchit variables, b:syng_str and
the foldexpr settings, and b:undo_indent for indent settings, instead of
relying on whichever indent file was loaded last.

ftplugin/vue.vim

@@ -1,8 +1,12 @@
 if exists("b:did_ftplugin") | finish | endif
 let b:did_ftplugin = 1
 
+let b:undo_ftplugin = (exists('b:undo_ftplugin') ? b:undo_ftplugin.' | ' : '')
+      \ . 'unlet! b:syng_str b:syng_strcom'
+
 if !has('nvim')
   setlocal matchpairs+=<:>
+  let b:undo_ftplugin .= ' | setlocal matchpairs<'
 endif
 
 if exists("loaded_matchit")
@@ -11,6 +15,7 @@ if exists("loaded_matchit")
         \ '<\@<=[ou]l\>[^>]*\%(>\|$\):<\@<=li\>:<\@<=/[ou]l>,' .
         \ '<\@<=dl\>[^>]*\%(>\|$\):<\@<=d[td]\>:<\@<=/dl>,' .
         \ '<\@<=\([^/][^ \t>]*\)[^>]*\%(>\|$\):<\@<=/\1>'
+  let b:undo_ftplugin .= ' | unlet! b:match_ignorecase b:match_words'
 endif
 
 " Indent correctly with template string for vim-javascript/built-in

ftplugin/vue/fold.vim

@@ -14,6 +14,8 @@ function! VueFoldMain(...)
 
     setlocal foldexpr=GetVueFold(v:lnum)
     setlocal foldmethod=expr
+    let b:undo_ftplugin = (exists('b:undo_ftplugin') ? b:undo_ftplugin.' | ' : '')
+          \ . 'setlocal foldexpr< foldmethod<'
   endif
 endfunction