vim-patch:8.1.2371: FEAT_TEXT_PROP is a confusing name (#35466)

Problem:    FEAT_TEXT_PROP is a confusing name.
Solution:   Use FEAT_PROP_POPUP. (Naruhiko Nishino, closes vim/vim#5291)

05ad5ff0ab

textprop,popuwin remain N/A features.
getchar.c has the relevant code changes.

Port runtest.vim changes from patch v8.1.1561.

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

src/nvim/eval/window.c

@@ -177,6 +177,7 @@ win_T *find_win_by_nr(typval_T *vp, tabpage_T *tp)
 
 /// Find a window: When using a Window ID in any tab page, when using a number
 /// in the current tab page.
+/// Returns NULL when not found.
 win_T *find_win_by_nr_or_id(typval_T *vp)
 {
   int nr = (int)tv_get_number_chk(vp, NULL);

src/nvim/getchar.c

@@ -2675,7 +2675,7 @@ static int vgetorpeek(bool advance)
 
           if (result == map_result_get) {
             // get a character: 2. from the typeahead buffer
-            c = typebuf.tb_buf[typebuf.tb_off] & 255;
+            c = typebuf.tb_buf[typebuf.tb_off];
             if (advance) {  // remove chars from tb_buf
               cmd_silent = (typebuf.tb_silent > 0);
               if (typebuf.tb_maplen > 0) {