Add SQLiteAdapter::isMemory helper function #1356

Job	Run time
Coding Standard & Static Analysis	22s
Windows - PHP 8.1 & SQL Server	3m 33s
testsuite (8.1, sqlite)	22s
testsuite (8.1, mysql)	38s
testsuite (8.1, pgsql)	45s
testsuite (8.4, sqlite)	21s
testsuite (8.4, mysql)	53s
testsuite (8.4, pgsql)	39s
testsuite (8.2, mysql)	52s
testsuite (8.1, sqlite, prefer-lowest)	20s
	8m 45s

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