h3: make grease_value() public (#1688) #4670

Job	Run time
quiche	3m 33s
quiche (boringssl-boring-crate)	3m 29s
quiche_ios (x86_64-apple-ios)	1m 52s
quiche_windows (x86_64-pc-windows-msvc)	2m 58s
quiche_ios (aarch64-apple-ios)	1m 50s
quiche_windows (i686-pc-windows-msvc)	5m 9s
quiche_windows (x86_64-pc-windows-gnu)	6m 12s
android_ndk_lts (aarch64-linux-android)	1m 44s
quiche_windows (i686-pc-windows-gnu)	5m 10s
android_ndk_lts (armv7-linux-androideabi)	1m 35s
docker	2m 18s
android_ndk_lts (x86_64-linux-android)	1m 40s
android_ndk_lts (i686-linux-android)	1m 34s
http3_test	1m 10s
nginx (1.16.1)	58s
quiche_macos	2m 56s
quiche_multiarch (aarch64-unknown-linux-gnu)	3m 20s
quiche_multiarch (armv7-unknown-linux-gnueabihf)	3m 38s
quiche_multiarch (i686-unknown-linux-gnu)	2m 23s
	53m 29s

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