Add Thread#internal_name= (#15298) #3548

Job	Run time
check_format	1m 37s
x86_64-gnu-test (1.7.3)	32m 31s
x86_64-gnu-test (1.8.2)	34m 11s
x86_64-gnu-test (1.9.2)	32m 17s
x86_64-gnu-test (1.10.1)	36m 34s
x86_64-gnu-test (1.11.2)	36m 33s
x86_64-gnu-test-preview_mt	5m 41s
x86_64-gnu-test (1.12.2)	33m 57s
x86_64-gnu-test (1.13.3)	33m 21s
x86_64-gnu-test (1.14.0)	33m 47s
x86_64-musl-test	36m 43s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	32m 30s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 15s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	34m 50s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	33m 3s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	35m 39s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	32m 37s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	32m 14s
	9h 11m 20s

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