PostAnalysis mode no longer eagerly reveals opaque types

[lcnr]

affected test

• tests/ui/type-alias-impl-trait/in-where-clause.rs

#![feature(type_alias_impl_trait)]
type Bar = impl Sized;

fn foo() -> Bar
where
    Bar: Send,
{
    [0; 1 + 2]
}

fn main() {}

This encounters a query cycle with the old solver as evaluating 1 + 2 ends up normalizing the where-clause Bar: Send, normalizing Bar relies on type checking foo as its a defining use. We encounter these cycles whenever there's an opaque type in a where-clause of its defining scope and we evaluate a constant during typeck.

The new solver does not eagerly normalize its ParamEnv when switching to post analysis, causing us to only fail with a cycle error when actually trying to use that where-bound.

[lcnr]

when stabilizing TAIT we should make sure that using them in the env is an error determinstically