Tools/build/stable_abi.py: Improve ergonomics (GH-105355)

* Tools/build/stable_abi.py: Improve ergonomics

- Make the manifest file argument optional
- Output resolved paths with --list (getting rid of `../../`)
- Mention --all or --generate-all if no actions are specified

* Don't hardcode Misc/stable_abi.toml in Makefile, rely on the default