* Add `flat-top` variants for `a`/`g`/`m`/`n`/`p`/`q`/`r`/`α`/`η`/`а`/`р` (#1269) (#2519).
* Add `flat-bottom` variants for `G`/`U`/`b`/`d`/`u`/`μ`/`µ`.
* Refine shape of the following characters:
  - LATIN CAPITAL LIGATURE OE (`U+0152`).
  - LATIN LETTER SMALL CAPITAL OE (`U+0276`).
  - MODIFIER LETTER SMALL CAPITAL OE (`U+107A3`).
