Strengthen check for UTF-8 conformity in formatContent() #626

Job	Run time
PHPUnit Composer v2 (PHP 7.4)	34s
PHPUnit coverage (PHP 7.4)	59s
PHPUnit (PHP 7.2)	31s
PHPUnit (PHP 7.3)	30s
PHPUnit (PHP 7.4)	29s
Tests alternative autoloader (PHP 7.1)	10s
PHPUnit (PHP 8.0)	27s
Tests alternative autoloader (PHP 7.2)	13s
PHPUnit (PHP 8.1)	30s
Tests alternative autoloader (PHP 7.3)	11s
PHPUnit (PHP 8.2)	30s
Tests alternative autoloader (PHP 7.4)	10s
Tests alternative autoloader (PHP 8.0)	6s
PHPUnit (PHP 8.3)	28s
Tests alternative autoloader (PHP 8.1)	7s
Tests alternative autoloader (PHP 8.2)	6s
PHPUnit (PHP 7.1)	32s
Tests alternative autoloader (PHP 8.3)	9s
PHPUnit lowest deps (PHP 7.3)	41s
Windows-Tests with PHP 7.1	1m 8s
Windows-Tests with PHP 7.2	52s
Windows-Tests with PHP 7.3	53s
Windows-Tests with PHP 7.4	56s
Windows-Tests with PHP 8.0	45s
Windows-Tests with PHP 8.1	59s
Windows-Tests with PHP 8.2	56s
Windows-Tests with PHP 8.3	50s
	14m 42s

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