Rename CSerAction* to Action*

Summary:
This allows new code, added in the next commit, to conform to the coding
guideline: No C-prefix for class names.

This is a partial backport of core#25284
https://github.com/bitcoin/bitcoin/pull/25284/commits/fac42e9d35f6ba046999b2e3a757ab720c51b6bb

Depends on D19054

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19055