Rename mempool method queryHashes to getAllTxIds

Summary: And use the TxId data type where appropriated. This is just a better name and explicity typing, with no change in behavior.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13119