ICU-22549 Add DateTimePatternGenerator fuzzer #1243

Job	Run time
clang-valgrind-test	10m 49s
clang-valgrind-intltest (utility)	6m 34s
clang-valgrind-intltest (normalize)	6m 30s
clang-valgrind-intltest (collator)	5m 11s
clang-valgrind-intltest (regex)	5m 20s
clang-valgrind-intltest (format)	16m 27s
clang-valgrind-intltest (translit)	6m 19s
clang-valgrind-intltest (rbbi)	7m 8s
clang-valgrind-intltest (rbnf)	6m 2s
clang-valgrind-intltest (rbnfrt)	6m 14s
clang-valgrind-intltest (icuserv)	5m 23s
clang-valgrind-intltest (idna)	4m 59s
clang-valgrind-intltest (convert)	6m 50s
clang-valgrind-intltest (rbnfp)	5m 17s
clang-valgrind-intltest (csdet)	5m 16s
clang-valgrind-intltest (spoof)	5m 5s
clang-valgrind-intltest (bidi)	5m 35s
	1h 54m 59s

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