Add support for 0x1fb90

Allocation in box_glyph_id is larger than necessary to account for the
addition of 0x1fb8c ... 0x1fb94 eventually, which are quite similar but
will require more work to add. Note that 0x1fb93 is not present in the
standard yet, but it is easy to guess what it will likely be from
context, so it should be kept in the allocation imo.

kitty/fonts/box_drawing.py

@@ -865,6 +865,7 @@ box_chars: Dict[str, List[Callable[[BufType, int, int], Any]]] = {
     '░': [p(shade, light=True)],
     '▒': [shade],
     '▓': [p(shade, light=True, invert=True)],
+    '🮐': [p(shade, invert=True)],
     '▔': [p(eight_bar, horizontal=True)],
     '▕': [p(eight_bar, which=7)],
     '▖': [p(quad, y=1)],