perf(extmarks): add metadata for efficient filtering of special decorations

This expands on the global "don't pay for what you don't use" rules for
these special extmark decorations:

- inline virtual text, which needs to be processed in plines.c when we
  calculate the size of text on screen
- virtual lines, which are needed when calculating "filler" lines
- signs, with text and/or highlights, both of which needs to be
  processed for the entire line already at the beginning of a line.

This adds a count to each node of the marktree, for how many special
marks of each kind can be found in the subtree for this node. This makes
it possible to quickly skip over these extra checks, when working in
regions of the buffer not containing these kind of marks, instead of
before where this could just be skipped if the entire _buffer_
didn't contain such marks.

src/nvim/drawline.c

@@ -32,6 +32,7 @@
 #include "nvim/highlight_group.h"
 #include "nvim/indent.h"
 #include "nvim/mark_defs.h"
+#include "nvim/marktree.h"
 #include "nvim/match.h"
 #include "nvim/mbyte.h"
 #include "nvim/memline.h"
@@ -1645,7 +1646,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
                                           &decor_state);
         }
 
-        if (!has_foldtext && wp->w_buffer->b_virt_text_inline > 0) {
+        if (!has_foldtext && buf_meta_total(wp->w_buffer, kMTMetaInline) > 0) {
           handle_inline_virtual_text(wp, &wlv, ptr - line);
           if (wlv.n_extra > 0 && wlv.virt_inline_hl_mode <= kHlModeReplace) {
             // restore search_attr and area_attr when n_extra is down to zero
@@ -1662,9 +1663,8 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
         }
       }
 
-      int *area_attr_p
-        = wlv.extra_for_extmark && wlv.virt_inline_hl_mode <= kHlModeReplace
-          ? &saved_area_attr : &area_attr;
+      int *area_attr_p = wlv.extra_for_extmark && wlv.virt_inline_hl_mode <= kHlModeReplace
+                         ? &saved_area_attr : &area_attr;
 
       // handle Visual or match highlighting in this line
       if (wlv.vcol == wlv.fromcol