If patch fails to apply, warn it is likely to fail to land and provide instructions how to resolve (#3222)

[Archaeopteryx]

No description provided.

[marco-c]

This would be a nice improvement for merge conflict resolution (even if it catches a small minority of cases: patches that have merge conflicts when posted to Phab).
We should report it as a warning to Lando too.

CC @cgsheeh @zzzeid @shtrom

[zzzeid]

This would be a nice improvement for merge conflict resolution (even if it catches a small minority of cases: patches that have merge conflicts when posted to Phab). We should report it as a warning to Lando too.

Couple of thoughts:

• This could be possible to do with small modifications on the code-review-bot side, since it currently posts a warning that static analysis is in progress, and later deletes that warning. Instead of deleting it, it could modify the text, or delete it and create a new one that shows the intended warning (no Lando change required here).
• I suspect that code-review-bot does not currently apply patches based on remote HEAD, which is what Lando currently does. This may cause some discrepancies in what can and can't be merged.