Character request: Medium shade half-blocks

It’s not a top priority, but it would be nice to have these four characters from the [_Symbols for Legacy Computing_ Uniode block](https://www.unicode.org/charts/PDF/U1FB00.pdf):
- 🮎 U+1FB8E UPPER HALF MEDIUM SHADE
- 🮏 U+1FB8F LOWER HALF MEDIUM SHADE
- 🮑 U+1FB91 UPPER HALF BLOCK AND LOWER HALF INVERSE MEDIUM SHADE
- 🮒 U+1FB92 UPPER HALF INVERSE MEDIUM SHADE AND LOWER HALF BLOCK

The issue names no source files, tests, or entry points. Start by locating the font source and build workflow, then compare existing block and shade glyphs with the Unicode chart linked in the issue. Done means U+1FB8E, U+1FB8F, U+1FB91, and U+1FB92 are included and render correctly in the project’s fonts.

Written by the indexing model from the issue text.