Better error message for editable installs with missing --no-build-isolation

Meson needs the `--no-build-isolation` flag for editable installs. I've stumbled over a missing `--no-build-isolation` flag multiple times when a project adopted meson but I followed old install instructions.

This results in a quite cryptic stack trace. Could meson detect an editable install with missing `--no-build-isolation` and issue a more informative warning?

The issue does not name a file, test, or entry point. Start by locating the editable-install handling in meson-python and reproduce the cryptic failure without --no-build-isolation; done means an informative warning is emitted for that case.

Written by the indexing model from the issue text.