vim-patch:8.1.1136: decoding of mouse click escape sequence is not tested (#35551)

Problem:    Decoding of mouse click escape sequence is not tested.
Solution:   Add a test for xterm and SGR using low-level input.  Make
            low-level input execution with feedkeys() work.

905dd905de

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/api/vim.c

@@ -332,7 +332,7 @@ void nvim_feedkeys(String keys, String mode, Boolean escape_ks)
     if (!dangerous) {
       ex_normal_busy++;
     }
-    exec_normal(true);
+    exec_normal(true, lowlevel);
     if (!dangerous) {
       ex_normal_busy--;
     }