Add tagbar#StopAutoUpdate

This is useful to stop updating information, after using
`tagbar#currenttag` manually/temporarily only.

autoload/tagbar.vim

@@ -862,8 +862,7 @@ function! s:CloseWindow() abort
     call s:ShrinkIfExpanded()
 
     if s:autocommands_done && !s:statusline_in_use
-        autocmd! TagbarAutoCmds
-        let s:autocommands_done = 0
+        call tagbar#StopAutoUpdate()
     endif
 
     call tagbar#debug#log('CloseWindow finished')
@@ -3243,6 +3242,11 @@ function! tagbar#RestoreSession() abort
     call s:RestoreSession()
 endfunction
 
+function! tagbar#StopAutoUpdate() abort
+    autocmd! TagbarAutoCmds
+    let s:autocommands_done = 0
+endfunction
+
 " }}}2
 
 " tagbar#toggle_pause() {{{2