Change ty and const error's pretty printing to be in braces
`[const error]` and `[type error]` are slightly confusing since they look like either a slice with an error type for the element ty or a slice with a const argument as the type ???. This PR changes them to display as `{const error}` and `{type error}` similar to `{integer}`.
This does not update the `Debug` impls for them which is done in #111988.
I updated some error logic to avoid printing the substs of trait refs when unable to resolve an assoc item for them, this avoids emitting errors with `{type error}` in them. The substs are not relevant for these errors since we don't take into account the substs when resolving the assoc item.
r? ``@compiler-errors``
a99209738e