ICU-22890 MF2: Add lone surrogate test to parser #2843

Job	Run time
clang-valgrind-intltest (utility)	6m 46s
clang-valgrind-test	10m 25s
clang-valgrind-intltest (normalize)	6m 39s
clang-valgrind-intltest (collator)	5m 35s
clang-valgrind-intltest (regex)	5m 26s
clang-valgrind-intltest (format)	16m 42s
clang-valgrind-intltest (translit)	6m 13s
clang-valgrind-intltest (rbbi)	8m 2s
clang-valgrind-intltest (rbnf)	6m 31s
clang-valgrind-intltest (rbnfrt)	6m 26s
clang-valgrind-intltest (icuserv)	5m 22s
clang-valgrind-intltest (idna)	5m 39s
clang-valgrind-intltest (convert)	7m 8s
clang-valgrind-intltest (rbnfp)	5m 41s
clang-valgrind-intltest (csdet)	5m 37s
clang-valgrind-intltest (spoof)	5m 20s
clang-valgrind-intltest (bidi)	5m 20s
	1h 58m 52s

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