ICU-22261 Add tech preview implementation for MessageFormat 2.0 to icu4c #1969

Job	Run time
clang-valgrind-intltest (utility)	6m 31s
clang-valgrind-test	10m 11s
clang-valgrind-intltest (normalize)	5m 55s
clang-valgrind-intltest (collator)	5m 7s
clang-valgrind-intltest (regex)	5m 34s
clang-valgrind-intltest (format)	16m 15s
clang-valgrind-intltest (translit)	5m 33s
clang-valgrind-intltest (rbbi)	7m 38s
clang-valgrind-intltest (rbnf)	6m 2s
clang-valgrind-intltest (rbnfrt)	6m 9s
clang-valgrind-intltest (icuserv)	5m 32s
clang-valgrind-intltest (idna)	4m 53s
clang-valgrind-intltest (convert)	7m 4s
clang-valgrind-intltest (rbnfp)	5m 9s
clang-valgrind-intltest (csdet)	5m 8s
clang-valgrind-intltest (spoof)	5m 17s
clang-valgrind-intltest (bidi)	5m 17s
	1h 53m 15s

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