runtime: deterministic fallback hashes across process boundary

[prattmic]

Map hashes use pre-process unique seeds to ensure that hashes differ across processes: aeskeysched for AES hash, and hashkey for fallback hash. Both are initialized in alginit.

https://go.dev/cl/516860 refactored the rand implementation in the runtime. Initialization of aeskeysched was changed to use bootstrapRand (available early), while hashkey was initialized with rand. rand's seed is not initialized until after alginit, so hashkey ends up with a deterministic value in every single process! Because hashkey is deterministic, so to are all (fallback) hashes.

cc @randall77 @rsc

[prattmic]

@gopherbot Please backport to 1.22. This regression makes map hashes deterministic across processes.

[gopherbot]

Backport issue(s) opened: #66886 (for 1.22).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/580136 mentions this issue: runtime: use bootstrapRand to initialize hashkey

[gopherbot]

Change https://go.dev/cl/580018 mentions this issue: [release-branch.go1.22] runtime: use bootstrapRand to initialize hashkey