ICU-22940 MF2 ICU4C: Error checking improvements in parser #173

Job	Run time
clang-valgrind-test	10m 31s
clang-valgrind-intltest (utility)	6m 41s
clang-valgrind-intltest (normalize)	6m 28s
clang-valgrind-intltest (collator)	5m 36s
clang-valgrind-intltest (regex)	5m 22s
clang-valgrind-intltest (format)	16m 24s
clang-valgrind-intltest (translit)	6m 20s
clang-valgrind-intltest (rbbi)	8m 7s
clang-valgrind-intltest (rbnf)	6m 23s
clang-valgrind-intltest (rbnfrt)	6m 35s
clang-valgrind-intltest (icuserv)	5m 26s
clang-valgrind-intltest (idna)	5m 42s
clang-valgrind-intltest (convert)	7m 45s
clang-valgrind-intltest (rbnfp)	5m 40s
clang-valgrind-intltest (csdet)	5m 5s
clang-valgrind-intltest (spoof)	5m 37s
clang-valgrind-intltest (bidi)	5m 28s
	1h 59m 10s

Provide feedback