Implement `tainted_by_errors` in MIR borrowck, use it to skip CTFE
Putting this up for initial review. The issue that I found is when we're evaluating a const, we're doing borrowck, but doing nothing with the fact that borrowck fails.
This implements a `tainted_by_errors` field for MIR borrowck like we have in infcx, so we can use that information to return an `Err` during const eval if our const fails to borrowck.
This PR needs some cleaning up. I should probably just use `Result` in more places, instead of `.expect`ing in the places I am, but I just wanted it to compile so I could see if it worked!
Fixes#93646
r? `@oli-obk`
feel free to reassign
9cdefd763b