Don't consider candidates with no failing where clauses when refining obligation causes in new solver

[compiler-errors]

Improves error messages when we have param-env candidates that don't deeply unify (i.e. after alias-bounds).

r? lcnr

[rustbot]

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

[compiler-errors]

@bors r=lcnr

[bors]

:pushpin: Commit 4e3350d43b2546281784d2ce4cf6803473a81645 has been approved by lcnr

It is now in the queue for this repository.

[bors]

:hourglass: Testing commit 4e3350d43b2546281784d2ce4cf6803473a81645 with merge 5a2bf5350f37756fc6be8f02b85e7724febeab4d...

[rust-log-analyzer]

The job armhf-gnu failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

```plain ```

[bors]

:broken_heart: Test failed - checks-actions

[lcnr]

@bors retry