ICU-22898 MF2: fix various parser bugs and add more tests #2863

Job	Run time
clang-valgrind-test	10m 33s
clang-valgrind-intltest (utility)	6m 44s
clang-valgrind-intltest (normalize)	6m 32s
clang-valgrind-intltest (collator)	5m 8s
clang-valgrind-intltest (regex)	5m 6s
clang-valgrind-intltest (format)	16m 9s
clang-valgrind-intltest (translit)	5m 51s
clang-valgrind-intltest (rbbi)	7m 48s
clang-valgrind-intltest (rbnf)	6m 21s
clang-valgrind-intltest (rbnfrt)	6m 19s
clang-valgrind-intltest (icuserv)	5m 26s
clang-valgrind-intltest (idna)	5m 22s
clang-valgrind-intltest (convert)	6m 50s
clang-valgrind-intltest (rbnfp)	5m 18s
clang-valgrind-intltest (csdet)	5m 10s
clang-valgrind-intltest (spoof)	5m 18s
clang-valgrind-intltest (bidi)	5m 42s
	1h 55m 37s

Provide feedback