DEV: Switch our fast_xor gem for xorcist (PR #10565)

We use the xor function as part of password hashing and we want to use a faster version than the native ruby xor’ing feature so we use a gem for this.

fast_xor has been abandoned, and xorcist fixed our initial holdup for switching in https://github.com/fny/xorcist/issues/4

xorcist also has jruby support so we can remove our jruby fallback logic.

Didn’t add any new tests here because we already have existing tests that should catch any issues.

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