Make getrandom feature imply rand_core so Generate doctests compile

[eligrubb]

Issue

Running cargo test (or cargo test --doc) on an individual crate fails to compile the usage doctest:

  error[E0432]: unresolved import `xaes_256_gcm::aead::Generate`
    --> xaes-256-gcm/src/lib.rs
     |
     |     aead::{Aead, AeadCore, Generate, Key, KeyInit},
     |                            ^^^^^^^^ no `Generate` in the root
     |
  note: found an item that was configured out
     | pub use common::{Generate, rand_core};
     |                  ^^^^^^^^   (gated behind the `rand_core` feature)

  error[E0599]: no associated function named `generate` found ...

See #755 for more details.

Fix

Generate is exported by aead under the aead/rand_core feature. Each AEAD crate currently enables the aead/rand_core feature only under their own rand_core feature. To fix, chain each crate's getrandom feature into its own rand_core feature, which transitively enables aead/rand_core:

  # before
  getrandom = ["aead/getrandom"]
  # after
  getrandom = ["aead/getrandom", "rand_core"]

This matches the mgm crate which already follows this convention.

Crates touched:

• aes-gcm, aes-gcm-siv, aes-siv, ascon-aead128, belt-dwp, ccm, chacha20poly1305, deoxys, eax, ocb3: ["aead/getrandom"] → ["aead/getrandom", "rand_core"]
• xaes-256-gcm: ["aes-gcm/getrandom"] → ["aead/getrandom", "aes-gcm/getrandom", "rand_core"]

Testing

• Each crate's doctests now pass standalone: cargo test --doc -p for all 11.
• cargo test --workspace still passes

Note

Alternative, simpler upstream fix may exist, all getrandom features already enable aead/getrandom. If upstream, aead feature aead/getrandom implied aead/rand_core, this would not be necessary. See traits PR#2450 for a proposal of how this would look.

[eligrubb]

Closing in favor of traits PR#2452 which solves this problem upstream. aead dependency version will need to be bumped before tests are fixed and #755 can be closed.