Generators: add tests covering handling of invalid docs #2350

Job	Run time
Coverage: 8.4 (Linux)	4m 21s
Coverage: 8.4 (Win)	1m 52s
Coverage: 5.4 (Linux)	27m 31s
Coverage: 5.5 (Win)	2m 35s
Coverage: 7.2 with custom ini settings (Linux)	6m 15s
Build Phar on PHP: 8.0 / Build Phar on PHP: 8.0	21s
PHP: 7.0 with custom ini settings (Linux)	1m 26s
PHP: 5.4 (Linux)	1m 59s
PHP: 5.5 with custom ini settings (Linux)	7m 16s
PHP: 5.5 (Linux)	8m 31s
PHP: 5.6 (Linux)	6m 52s
PHP: 7.0 (Linux)	1m 51s
PHP: 7.1 (Linux)	1m 33s
PHP: 7.2 (Linux)	1m 23s
PHP: 7.3 (Linux)	53s
PHP: 7.4 (Linux)	1m 1s
PHP: 8.0 (Linux)	54s
PHP: 8.1 (Linux)	1m 0s
PHP: 8.2 (Linux)	52s
PHP: 8.3 (Linux)	57s
PHP: 8.4 (Linux)	31s
PHP: 8.5 (Linux)	51s
PHP: 5.5 (Win)	1m 41s
PHP: 5.6 (Win)	6m 38s
PHP: 7.0 (Win)	1m 55s
PHP: 7.1 (Win)	1m 40s
PHP: 7.2 (Win)	1m 24s
PHP: 7.3 (Win)	1m 1s
PHP: 7.4 (Win)	53s
PHP: 8.0 (Win)	54s
PHP: 8.1 (Win)	50s
PHP: 8.2 (Win)	51s
PHP: 8.3 (Win)	51s
PHP: 8.4 (Win)	28s
PHP: 8.5 (Win)	50s
coveralls-finish	4s
	1h 40m 45s

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