ICU-22940 MF2 ICU4C: Error checking improvements in parser #3213

Job	Run time
clang-valgrind-test	10m 23s
clang-valgrind-intltest (utility)	6m 46s
clang-valgrind-intltest (normalize)	6m 11s
clang-valgrind-intltest (collator)	5m 16s
clang-valgrind-intltest (regex)	5m 25s
clang-valgrind-intltest (format)	16m 24s
clang-valgrind-intltest (translit)	5m 51s
clang-valgrind-intltest (rbbi)	8m 20s
clang-valgrind-intltest (rbnf)	6m 32s
clang-valgrind-intltest (rbnfrt)	6m 24s
clang-valgrind-intltest (icuserv)	5m 25s
clang-valgrind-intltest (idna)	5m 24s
clang-valgrind-intltest (convert)	6m 48s
clang-valgrind-intltest (rbnfp)	5m 20s
clang-valgrind-intltest (csdet)	5m 29s
clang-valgrind-intltest (spoof)	5m 13s
clang-valgrind-intltest (bidi)	5m 46s
	1h 56m 57s

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