Alt+H, O, A (AutoFit Row Height) and Alt+H, O, I (AutoFit Column Width)
ran nothing when Alt was still held for H, as Excel allows: any key with
Alt down cancelled keytips. KeyTips now tracks the left Alt key, and a
letter typed with it held that continues a known sequence is handled as
a keytip letter. Other Alt combinations still cancel; AltGr (right Alt)
and macOS Option are unchanged (#1864).