93266: kvserver: refactor replicaAppBatch for standalone log application r=pavelkalinnikov a=tbg

This long (but individually small) sequence of commits moves `(*replicaAppBatch).Stage` close to the structure that was prototyped in #93265, where it has the following steps:

- command checks (standalone)
- testing interceptors (replica)
- pre-add triggers (standalone)
- pre-add triggers (replica)
- add (to pebble batch, standalone)
- post-add triggers (standalone)
- post-add triggers (replica)

In standalone application (e.g. for #93244) we'd use an `apply.Batch` that is an `appBatch`, instead of a `replicaAppBatch`, i.e. skip all of the (replica) steps above.

This PR doesn't get us all the way there - we still need to tease apart the `post-add triggers (replica)` step, which currently contains code that should be in `post-add triggers (standalone)`; this is best tackled in a separate PR since it's going to be quite a bit of work.

Touches #75729.

Epic: CRDB-220
Release note: None

Co-authored-by: Tobias Grieger <tobias.b.grieger@gmail.com>