ICU-23002 Fix int64_t overflow in NFRule::parseRuleDescriptor #3277

Job	Run time
clang-valgrind-intltest (utility)	6m 51s
clang-valgrind-test	10m 18s
clang-valgrind-intltest (normalize)	7m 9s
clang-valgrind-intltest (collator)	5m 23s
clang-valgrind-intltest (regex)	5m 47s
clang-valgrind-intltest (format)	10m 31s
clang-valgrind-intltest (translit)	6m 1s
clang-valgrind-intltest (rbbi)	8m 1s
clang-valgrind-intltest (rbnf)	6m 25s
clang-valgrind-intltest (rbnfrt)	6m 24s
clang-valgrind-intltest (icuserv)	5m 13s
clang-valgrind-intltest (idna)	5m 21s
clang-valgrind-intltest (convert)	6m 53s
clang-valgrind-intltest (rbnfp)	6m 46s
clang-valgrind-intltest (csdet)	5m 35s
clang-valgrind-intltest (spoof)	5m 54s
clang-valgrind-intltest (bidi)	5m 31s
	1h 54m 3s

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