expr: fix regex matching on inputs containing newlines #18178

Job	Run time
Build and test uufuzz examples	1m 46s
Build the fuzzers	2m 57s
Fuzz (fuzz_printf, true)	3m 54s
Fuzz (fuzz_seq, false)	1m 15s
Fuzz (fuzz_test, true)	3m 47s
Fuzz (fuzz_expr, true)	3m 55s
Fuzz (fuzz_date, true)	3m 52s
Fuzz (fuzz_split, false)	2m 52s
Fuzz (fuzz_parse_glob, true)	3m 55s
Fuzz (fuzz_seq_parse_number, false)	2m 48s
Fuzz (fuzz_wc, false)	2m 53s
Fuzz (fuzz_env, false)	58s
Fuzz (fuzz_cut, false)	3m 20s
Fuzz (fuzz_parse_time, false)	1m 23s
Fuzz (fuzz_dirname, true)	3m 53s
Fuzz (fuzz_cksum, false)	2m 47s
Fuzz (fuzz_sort, false)	3m 19s
Fuzz (fuzz_tr, false)	3m 43s
Fuzz (fuzz_parse_size, false)	59s
Fuzz (fuzz_echo, true)	4m 16s
Fuzz (fuzz_non_utf8_paths, true)	3m 42s
Fuzzing Summary	10s
	1h 2m 24s

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