ICU-22261 Add UCONFIG_NO_MF2 flag that can be used to disable MessageFormat 2 functionality #1981

Job	Run time
clang-valgrind-test	9m 56s
clang-valgrind-intltest (utility)	7m 7s
clang-valgrind-intltest (normalize)	6m 24s
clang-valgrind-intltest (collator)	5m 1s
clang-valgrind-intltest (regex)	5m 27s
clang-valgrind-intltest (format)	16m 59s
clang-valgrind-intltest (translit)	5m 33s
clang-valgrind-intltest (rbbi)	6m 53s
clang-valgrind-intltest (rbnf)	6m 16s
clang-valgrind-intltest (rbnfrt)	6m 23s
clang-valgrind-intltest (icuserv)	5m 30s
clang-valgrind-intltest (idna)	5m 18s
clang-valgrind-intltest (convert)	6m 38s
clang-valgrind-intltest (rbnfp)	5m 6s
clang-valgrind-intltest (csdet)	5m 21s
clang-valgrind-intltest (spoof)	5m 45s
clang-valgrind-intltest (bidi)	5m 9s
	1h 54m 46s

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