Allow constants to start with non-ascii uppercase and titlecase #12692

Job	Run time
check_format	1m 32s
x86_64-gnu-test (1.7.3)	34m 57s
x86_64-gnu-test (1.8.2)	36m 1s
x86_64-gnu-test (1.9.2)	33m 57s
x86_64-gnu-test (1.10.1)	36m 2s
x86_64-gnu-test (1.11.2)	33m 35s
x86_64-gnu-test (1.12.2)	34m 10s
x86_64-gnu-test (1.13.3)	34m 21s
x86_64-gnu-test (1.14.0)	33m 35s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	32m 52s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	34m 31s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	32m 39s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	34m 36s
x86_64-gnu-test-preview_mt	5m 36s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	34m 45s
x86_64-musl-test	36m 24s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	36m 22s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	32m 17s
	9h 18m 12s

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