ICU-22940 MF2 ICU4C: Error checking improvements in parser #3332

Job	Run time
clang-valgrind-test	10m 18s
clang-valgrind-intltest (utility)	6m 49s
clang-valgrind-intltest (normalize)	6m 16s
clang-valgrind-intltest (collator)	5m 27s
clang-valgrind-intltest (regex)	5m 28s
clang-valgrind-intltest (format)	16m 32s
clang-valgrind-intltest (translit)	5m 55s
clang-valgrind-intltest (rbbi)	8m 11s
clang-valgrind-intltest (rbnf)	6m 55s
clang-valgrind-intltest (rbnfrt)	6m 18s
clang-valgrind-intltest (icuserv)	5m 13s
clang-valgrind-intltest (idna)	5m 43s
clang-valgrind-intltest (convert)	6m 53s
clang-valgrind-intltest (rbnfp)	5m 26s
clang-valgrind-intltest (csdet)	5m 5s
clang-valgrind-intltest (spoof)	5m 14s
clang-valgrind-intltest (bidi)	5m 51s
	1h 57m 34s

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