tls_provider_init(): Rename prov_ctx to xor_prov_ctx to clarify #21229

Job	Run time
run-checker (no-atexit)	4m 48s
run-checker (no-cmp)	4m 37s
run-checker (no-cms)	4m 42s
run-checker (no-dgram)	4m 29s
run-checker (no-dh)	4m 38s
run-checker (no-dtls)	4m 51s
run-checker (no-ec)	4m 14s
run-checker (no-ecx)	4m 43s
run-checker (no-http)	4m 37s
run-checker (no-legacy)	4m 44s
run-checker (no-sock)	4m 20s
run-checker (enable-ssl-trace)	5m 9s
run-checker (no-stdio)	2m 11s
run-checker (no-threads)	4m 39s
run-checker (no-thread-pool)	4m 44s
run-checker (no-default-thread-pool)	5m 16s
run-checker (no-tls)	4m 23s
run-checker (no-tls1_2)	4m 38s
run-checker (no-tls1_3)	4m 26s
run-checker (enable-trace enable-fips)	5m 21s
run-checker (no-ui)	5m 5s
run-checker (no-quic)	4m 43s
	1h 41m 18s

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