R1:e8083ad63a32

Increase the storage size for commit summaries

Summary:
Fixes T11453. Currently, commit message summaries are limited to 80 bytes. This may only be 20-40 characters for CJK languages or langauges with Cyrillic script.

Increase storage size to 255, then truncate to the shorter of 255 bytes or 80 glyphs. This preserves the same behavior for latin languages, but is less tight for Russian, etc.

Some minor additional changes:

- Provide a way to ask "how much data fits in this column?" so we don't have to…