ICU-23053 In the ICU4X mode of the collation builder, mark middle starters in contractions #3588

Job	Run time
clang-valgrind-test	10m 29s
clang-valgrind-intltest (utility)	7m 25s
clang-valgrind-intltest (normalize)	6m 51s
clang-valgrind-intltest (collator)	5m 58s
clang-valgrind-intltest (regex)	5m 58s
clang-valgrind-intltest (format)	16m 47s
clang-valgrind-intltest (translit)	6m 9s
clang-valgrind-intltest (rbbi)	10m 0s
clang-valgrind-intltest (rbnf)	6m 54s
clang-valgrind-intltest (rbnfrt)	7m 16s
clang-valgrind-intltest (icuserv)	5m 57s
clang-valgrind-intltest (idna)	6m 13s
clang-valgrind-intltest (convert)	6m 50s
clang-valgrind-intltest (rbnfp)	5m 45s
clang-valgrind-intltest (csdet)	5m 57s
clang-valgrind-intltest (spoof)	5m 48s
clang-valgrind-intltest (bidi)	6m 2s
	2h 6m 19s

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