vim-patch:8.2.4401: map listing does not clear the rest of the command line

Problem:    Map listing does not clear the rest of the command line.
Solution:   Call msg_clear_eos(). (closes vim/vim#5623, closes vim/vim#5962)
d288eaad84

src/nvim/getchar.c

@@ -3519,6 +3519,7 @@ static void showmap(mapblock_T *mp, bool local)
   if (p_verbose > 0) {
     last_set_msg(mp->m_script_ctx);
   }
+  msg_clr_eos();
   ui_flush();                          // show one line at a time
 }
 

src/nvim/testdir/test_mapping.vim

@@ -474,7 +474,6 @@ func Test_expr_map_restore_cursor()
   END
   call writefile(lines, 'XtestExprMap')
   let buf = RunVimInTerminal('-S XtestExprMap', #{rows: 10})
-  call term_wait(buf)
   call term_sendkeys(buf, "\<C-B>")
   call VerifyScreenDump(buf, 'Test_map_expr_1', {})
 
@@ -483,6 +482,22 @@ func Test_expr_map_restore_cursor()
   call delete('XtestExprMap')
 endfunc
 
+func Test_map_listing()
+  CheckScreendump
+
+  let lines =<< trim END
+      nmap a b
+  END
+  call writefile(lines, 'XtestMapList')
+  let buf = RunVimInTerminal('-S XtestMapList', #{rows: 6})
+  call term_sendkeys(buf, ":                      nmap a\<CR>")
+  call VerifyScreenDump(buf, 'Test_map_list_1', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XtestMapList')
+endfunc
+
 func Test_expr_map_error()
   CheckScreendump
 
@@ -499,7 +514,6 @@ func Test_expr_map_error()
   END
   call writefile(lines, 'XtestExprMap')
   let buf = RunVimInTerminal('-S XtestExprMap', #{rows: 10})
-  call TermWait(buf)
   call term_sendkeys(buf, "\<F2>")
   call TermWait(buf)
   call term_sendkeys(buf, "\<CR>")