Make BerkeleyBatch::Recover and WalletBatch::RecoverKeysOnlyFilter standalone

Summary:

Instead of having these be class static functions, just make them be
standalone. Also removes WalletBatch::Recover which just passed through
to BerkeleyBatch::Recover.

Partial backport (8/11) of core PR18918:
https://github.com/bitcoin/bitcoin/pull/18918/commits/b426c7764d26e280e1f814cf36e050743c45cd12

Depends on D8594.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8595