feat(ui): inline virtual text

vim-patch:9.0.0067: cannot show virtual text

Problem:    Cannot show virtual text.
Solution:   Initial changes for virtual text support, using text properties.

7f9969c559

vim-patch:9.0.0116: virtual text not displayed if 'signcolumn' is "yes"

Problem:    Virtual text not displayed if 'signcolumn' is "yes".
Solution:   Set c_extra and c_final to NUL.
711483cd13

Co-authored-by: bfredl <bjorn.linse@gmail.com>

src/nvim/plines.h

@@ -11,9 +11,11 @@ typedef struct {
   win_T *cts_win;
   char *cts_line;    // start of the line
   char *cts_ptr;     // current position in line
+  int cts_row;
 
   bool cts_has_virt_text;  // true if if a property inserts text
   int cts_cur_text_width;     // width of current inserted text
+  MarkTreeIter cts_iter[1];
   // TODO(bfredl): iterator in to the marktree for scanning virt text
 
   int cts_vcol;    // virtual column at current position