Draft: cat-file: Switch to using `--batch-command`

Currently both ObjectReader and ObjectInfoReader use the --batch and --batch-check command. With the newly introduced --batch-command in git (v2.36). We could merge the two into one command which does both. This would remove the need for having two processes running and would also clean up code around flushing.

In this commit we setup the the base by moving both ObjectReader and ObjectInfoReader to using --batch-command. This also means that clients using the RequestRevision will now have to explicitly provide the type of data they're requesting (i.e. info or contents).

In the upcoming commits we'll slowly move all functionality of ObjectInfoReader to ObjectReader and deprecate ObjectInfoReader.

Part #4420 (closed)