False positive for Drupal.Files.LineLength for multibyte characters

Problem/Motivation

Discovered while working on this: #2572709: [meta] Fix 'Drupal.Files.LineLength' coding standard

Install drupal/coder, add Drupal.Files.LineLength to phpcs.xml.dist and do this:

../vendor/bin/phpcs -p -s lib/Drupal/Component/Utility/Html.php

You'll see this output:

FILE: ...Users/paul/pj2/drupal/core/lib/Drupal/Component/Utility/Html.php
----------------------------------------------------------------------
FOUND 0 ERRORS AND 6 WARNINGS AFFECTING 6 LINES
----------------------------------------------------------------------
 103 | WARNING | Line exceeds 80 characters; contains 91 characters
     |         | (Drupal.Files.LineLength.TooLong)
 199 | WARNING | Line exceeds 80 characters; contains 82 characters
     |         | (Drupal.Files.LineLength.TooLong)
 202 | WARNING | Line exceeds 80 characters; contains 82 characters
     |         | (Drupal.Files.LineLength.TooLong)
 203 | WARNING | Line exceeds 80 characters; contains 82 characters
     |         | (Drupal.Files.LineLength.TooLong)
 351 | WARNING | Line exceeds 80 characters; contains 82 characters
     |         | (Drupal.Files.LineLength.TooLong)
 386 | WARNING | Line exceeds 80 characters; contains 104 characters
     |         | (Drupal.Files.LineLength.TooLong)
----------------------------------------------------------------------

Line 351 contains multi-byte characters, and is under 80 chars when you look at it, but is presumably an edge case if you just count bytes:

   * will convert "é" to "é", whereas Html::escape() will not convert "é"

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes