R1:384b670709aa

Fix string truncation calls all over the codebase.

Summary: Fixes T6608, though I'll also clean up the comment for PhutilStringTruncator in another diff. If I understand correctly, before T1191, MySQL column length was by character count and post T1191 its by byte count. Ergo, most of these changes are going from codepoint -> bytes. See test plan for complete list of what was and was not done.

Test Plan:
Thought very carefully about each callsite and made changes as appropos. "Display" means the string…