ICU-22890 MF2: Add lone surrogate test to parser #2847

Job	Run time
clang-valgrind-test	10m 23s
clang-valgrind-intltest (utility)	7m 34s
clang-valgrind-intltest (normalize)	6m 8s
clang-valgrind-intltest (collator)	5m 29s
clang-valgrind-intltest (regex)	5m 17s
clang-valgrind-intltest (format)	16m 20s
clang-valgrind-intltest (translit)	6m 12s
clang-valgrind-intltest (rbbi)	7m 32s
clang-valgrind-intltest (rbnf)	6m 25s
clang-valgrind-intltest (rbnfrt)	6m 2s
clang-valgrind-intltest (icuserv)	5m 12s
clang-valgrind-intltest (idna)	5m 17s
clang-valgrind-intltest (convert)	7m 25s
clang-valgrind-intltest (rbnfp)	5m 36s
clang-valgrind-intltest (csdet)	5m 18s
clang-valgrind-intltest (spoof)	5m 19s
clang-valgrind-intltest (bidi)	5m 41s
	1h 57m 10s

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