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.

Thought very carefully about each callsite and made changes as appropos. "Display" means the string is clearly used for display-only purposes and correctly uses "glyph" already.

grep -rn PhutilUTF8StringTruncator *

applications/calendar/query/PhabricatorCalendarEventSearchEngine.php:217: ->addAttribute(id(new PhutilUTF8StringTruncator()) -- display
applications/chatlog/controller/PhabricatorChatLogChannelLogController.php:111: $author = id(new PhutilUTF8StringTruncator()) -- display
applications/conduit/method/ConduitConnectConduitAPIMethod.php:62: $client_description = id(new PhutilUTF8StringTruncator()) -- was codepoint, changed to bytes
applications/conpherence/view/ConpherenceFileWidgetView.php:22: ->setFileName(id(new PhutilUTF8StringTruncator()) -- display
applications/differential/controller/DifferentialDiffViewController.php:65: id(new PhutilUTF8StringTruncator()) -- display
applications/differential/event/DifferentialHovercardEventListener.php:69: id(new PhutilUTF8StringTruncator()) -- display
applications/differential/parser/DifferentialCommitMessageParser.php:144: $short = id(new PhutilUTF8StringTruncator()) -- was glyphs, made to bytes
applications/differential/view/DifferentialLocalCommitsView.php:80: $summary = id(new PhutilUTF8StringTruncator()) -- display
applications/diffusion/controller/DiffusionBrowseFileController.php:686: id(new PhutilUTF8StringTruncator()) -- display
applications/feed/story/PhabricatorFeedStory.php:392: $text = id(new PhutilUTF8StringTruncator()) -- display, unless people are saving the results of renderSummary() somewhere...
applications/harbormaster/storage/build/HarbormasterBuild.php:216: $log_source = id(new PhutilUTF8StringTruncator()) -- was codepoints now bytes
applications/herald/storage/transcript/HeraldObjectTranscript.php:55: // NOTE: PhutilUTF8StringTruncator has huge runtime for giant strings. -- not applicable
applications/maniphest/export/ManiphestExcelDefaultFormat.php:107: id(new PhutilUTF8StringTruncator()) -- bytes
applications/metamta/storage/PhabricatorMetaMTAMail.php:587: $body = id(new PhutilUTF8StringTruncator()) -- bytes
applications/people/event/PhabricatorPeopleHovercardEventListener.php:62: id(new PhutilUTF8StringTruncator()) -- display
applications/phame/conduit/PhameCreatePostConduitAPIMethod.php:93: id(new PhutilUTF8StringTruncator()) -- was codepoints, now bytes
applications/pholio/storage/PholioTransaction.php:300: id(new PhutilUTF8StringTruncator()) -- display
applications/phortune/provider/PhortuneBalancedPaymentProvider.php:147: $charge_as = id(new PhutilUTF8StringTruncator()) -- bytes
applications/ponder/storage/PonderAnswerTransaction.php:86: id(new PhutilUTF8StringTruncator()) -- display
applications/ponder/storage/PonderQuestionTransaction.php:267: id(new PhutilUTF8StringTruncator()) -- display
applications/ponder/storage/PonderQuestionTransaction.php:276: id(new PhutilUTF8StringTruncator()) -- display
applications/repository/storage/PhabricatorRepositoryCommitData.php:43: $summary = id(new PhutilUTF8StringTruncator()) -- was codepoints, now bytes
applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php:20: $data->setAuthorName(id(new PhutilUTF8StringTruncator()) -- was codepoints, now bytes
applications/slowvote/query/PhabricatorSlowvoteSearchEngine.php:158: $item->addAttribute(id(new PhutilUTF8StringTruncator()) -- display
infrastructure/daemon/workers/query/PhabricatorWorkerLeaseQuery.php:317: $host = id(new PhutilUTF8StringTruncator()) -- bytes
view/form/control/AphrontFormPolicyControl.php:61: $policy_short_name = id(new PhutilUTF8StringTruncator()) -- glyphs, probably display only