renderer: constrain dingbats category to cell size

Dingbats are generally symbolic glyphs that frequently overflow the
cell. Their defined codepoint width is "1" so they take one cell but
very often overflow to the next.

This extends the previously created logic for Nerd Font symbols such
that when a dingbat is next to whitespace, we allow it to use the full
size, but when a dingbat is next to an occupied cell we constrain it to
the cell size.

src/renderer/cell.zig

@@ -41,7 +41,9 @@ pub fn fgMode(
         // the subsequent character is empty, then we allow it to use
         // the full glyph size. See #1071.
         .text => text: {
-            if (!ziglyph.general_category.isPrivateUse(@intCast(cell.char))) {
+            if (!ziglyph.general_category.isPrivateUse(@intCast(cell.char)) and
+                !ziglyph.blocks.isDingbats(@intCast(cell.char)))
+            {
                 break :text .normal;
             }