Rename public interfaces from Tx to Inv in InvRequestTracker

Summary:
It renames the existing interfaces to reflect the file intent.

Depends on D9561.

Test Plan:

ninja all check-all
ninja bitcoin-fuzzers

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Maniphest Tasks: T1611

Differential Revision: https://reviews.bitcoinabc.org/D9562