fix(tmp buf): Keep clipboard contents

If Vim synchronizes contents in the un-named register and the
system clipboard via setting the `clipboard` option, making a
temporary buffer breaks the clipboard contents because it
overwrites the un-named register with original file contents.
So keep the contents by storing into a temporary variable and
restoring it after file type detection.

autoload/chezmoi/filetype.vim

@@ -179,12 +179,18 @@ function! s:run_default_detect(detect_target) abort
     let evignore_save = &eventignore
     let bufhidden_save = &bufhidden
     let l:cpo_save = &cpo
+    let l:clipboard_save = &clipboard
+    let l:reg_content_save = getreg('"')
+    let l:reg_type_save = getregtype('"')
 
     let bufnr_org = bufnr()
 
     try
       set eventignore=all
 
+      " Disable clipboard
+      set clipboard=
+
       " Enable to move to other buffer.
       set bufhidden=hide
 
@@ -214,6 +220,8 @@ function! s:run_default_detect(detect_target) abort
       let &eventignore = evignore_save
       let &bufhidden = bufhidden_save
       let &cpo = l:cpo_save
+      call setreg('""', l:reg_content_save, l:reg_type_save)
+      let &clipboard = l:clipboard_save
     endtry
   else
     execute 'doau filetypedetect BufRead ' . fnameescape(a:detect_target)