ICU-22940 MF2 ICU4C: Error checking improvements in parser #3331

Job	Run time
clang-valgrind-test	10m 15s
clang-valgrind-intltest (utility)	6m 51s
clang-valgrind-intltest (normalize)	6m 19s
clang-valgrind-intltest (collator)	5m 26s
clang-valgrind-intltest (regex)	5m 25s
clang-valgrind-intltest (format)	16m 40s
clang-valgrind-intltest (translit)	5m 55s
clang-valgrind-intltest (rbbi)	7m 54s
clang-valgrind-intltest (rbnf)	6m 29s
clang-valgrind-intltest (rbnfrt)	6m 26s
clang-valgrind-intltest (icuserv)	5m 17s
clang-valgrind-intltest (idna)	5m 25s
clang-valgrind-intltest (convert)	6m 50s
clang-valgrind-intltest (rbnfp)	5m 37s
clang-valgrind-intltest (csdet)	5m 25s
clang-valgrind-intltest (spoof)	5m 24s
clang-valgrind-intltest (bidi)	5m 39s
	1h 57m 17s

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