Generators: add tests covering handling of unsupported doc structures #2134

Job	Run time
Build Phar on PHP: 8.0	30s
Coverage: 8.4 (Linux)	4m 26s
Coverage: 8.4 (Win)	1m 45s
Coverage: 5.4 (Linux)	25m 34s
Coverage: 5.5 (Win)	2m 30s
Coverage: 7.2 with custom ini settings (Linux)	5m 55s
PHP: 5.4 (Linux)	1m 14s
PHP: 5.5 (Linux)	7m 28s
PHP: 5.6 (Linux)	6m 5s
PHP: 7.0 (Linux)	1m 31s
PHP: 7.1 (Linux)	1m 25s
PHP: 7.2 (Linux)	1m 32s
PHP: 7.3 (Linux)	51s
PHP: 7.4 (Linux)	53s
PHP: 8.0 (Linux)	58s
PHP: 8.1 (Linux)	55s
PHP: 8.2 (Linux)	1m 10s
PHP: 8.3 (Linux)	1m 13s
PHP: 8.4 (Linux)	34s
PHP: 8.5 (Linux)	1m 17s
PHP: 5.5 (Win)	1m 6s
PHP: 5.6 (Win)	5m 56s
PHP: 7.0 (Win)	1m 31s
PHP: 7.1 (Win)	1m 39s
PHP: 7.2 (Win)	1m 20s
PHP: 7.3 (Win)	58s
PHP: 7.4 (Win)	49s
PHP: 8.0 (Win)	53s
PHP: 8.1 (Win)	50s
PHP: 8.2 (Win)	56s
PHP: 8.3 (Win)	52s
PHP: 8.4 (Win)	36s
PHP: 8.5 (Win)	56s
PHP: 5.5 with custom ini settings (Linux)	6m 37s
PHP: 7.0 with custom ini settings (Linux)	1m 2s
coveralls-finish	2s
	1h 33m 49s

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