patch 8.1.1223: middle mouse click test fails without a clipboard

Problem:    Middle mouse click test fails without a clipboard.
Solution:   Check if the clipboard can be used. (Dominique Pelle, Christian
            Brabandt)  Also use WorkingClipboard() instead of checking for the
            "clipboard" feature.

src/testdir/test_quotestar.vim

@@ -1,6 +1,7 @@
 " *-register (quotestar) tests
 
-if !has('clipboard')
+source shared.vim
+if !WorkingClipboard()
   finish
 endif
 

src/testdir/test_termcodes.vim

@@ -5,6 +5,8 @@ if has('gui_running') || !has('unix')
   finish
 endif
 
+source shared.vim
+
 " Helper function to emit a terminal escape code.
 func TerminalEscapeCode(code_xterm, code_sgr, row, col, m)
   if &ttymouse ==# 'xterm2'
@@ -77,6 +79,10 @@ func Test_xterm_mouse_left_click()
 endfunc
 
 func Test_xterm_mouse_middle_click()
+  if !WorkingClipboard()
+    throw 'Skipped: No working clipboard'
+  endif
+
   new
   let save_mouse = &mouse
   let save_term = &term

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1223,
 /**/
     1222,
 /**/