ICU-22831 Fix memLeak in number_longnames.cpp by using LocalPointer #2473

Job	Run time
clang-valgrind-intltest (utility)	6m 47s
clang-valgrind-test	11m 26s
clang-valgrind-intltest (normalize)	6m 14s
clang-valgrind-intltest (collator)	5m 5s
clang-valgrind-intltest (regex)	5m 34s
clang-valgrind-intltest (format)	16m 42s
clang-valgrind-intltest (translit)	7m 0s
clang-valgrind-intltest (rbbi)	7m 16s
clang-valgrind-intltest (rbnf)	6m 30s
clang-valgrind-intltest (rbnfrt)	6m 6s
clang-valgrind-intltest (icuserv)	4m 57s
clang-valgrind-intltest (idna)	5m 40s
clang-valgrind-intltest (convert)	6m 22s
clang-valgrind-intltest (rbnfp)	5m 58s
clang-valgrind-intltest (csdet)	6m 24s
clang-valgrind-intltest (spoof)	5m 39s
clang-valgrind-intltest (bidi)	5m 14s
	1h 58m 54s

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