[TASK] Mark `OutputFormatter` as `@internal` #1969

Job	Run time
PHP Lint (7.2)	12s
PHP Lint (7.3)	12s
PHP Lint (7.4)	11s
PHP Lint (8.0)	10s
PHP Lint (8.1)	21s
PHP Lint (8.2)	18s
PHP Lint (8.3)	36s
PHP Lint (8.4)	30s
Static Analysis (composer:normalize, 8.3)	29s
Unit tests (7.2)	15s
Static Analysis (php:fixer, 8.3)	30s
Unit tests (7.3)	11s
Static Analysis (php:stan, 8.3)	30s
Unit tests (7.4)	19s
Static Analysis (php:rector, 8.3)	58s
Unit tests (8.0)	12s
Unit tests (8.1)	22s
Unit tests (8.2)	19s
Unit tests (8.3)	19s
Unit tests (8.4)	21s
	7m 15s

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