Start to overhaul RAND API

Remove unused rand_hw_xor, MD/EVP indirection
Make rand_pseudo same as rand.
Cleanup formatting and ifdef control
Rename some things:
    - rand_meth to openssl_rand_meth; make it global
    - source file
    - lock/init functions, start per-thread state
    - ossl_meth_init to ossl_rand_init
Put state into RAND_STATE structure
And put OSSL_RAND_STATE into ossl_typ.h
Use "randomness" instead of "entropy"

Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/3758)