http2: add headersDistinct to Http2ServerRequest fixes #64060 #8340

Job	Run time
Build slim tarball	2m 12s
aarch64-linux: Cache V8 build	23s
x86_64-darwin: with shared libraries	43m 8s
x86_64-linux: with shared libraries	32m 11s
aarch64-darwin: with shared libraries	25m 47s
aarch64-linux: with shared openssl-1.1.1w	22m 13s
aarch64-linux: with shared openssl-4.0.0	27m 7s
aarch64-linux: with shared openssl-3.5.6	26m 51s
aarch64-linux: with shared openssl-3.0.20	27m 15s
aarch64-linux: with shared openssl-3.6.2	23m 56s
aarch64-linux: with shared boringssl-0.20260526.0	23m 32s
	4h 14m 35s

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