[NLL] No "expected ..., found ..." in diagnostics

[jackh726]

This happens in a lot of tests, but from src/test/ui/traits/trait-upcasting/type-checking-test-4.rs:

before

error[E0308]: mismatched types
  --> $DIR/type-checking-test-4.rs:20:13
   |
LL |     let _ = x as &dyn Bar<'static, 'a>; // Error
   |             ^ lifetime mismatch
   |
   = note: expected trait object `dyn Bar<'static, 'a>`
              found trait object `dyn Bar<'static, 'static>`
note: the lifetime `'a` as defined here...
  --> $DIR/type-checking-test-4.rs:19:16
   |
LL | fn test_wrong1<'a>(x: &dyn Foo<'static>, y: &'a u32) {
   |                ^^
   = note: ...does not necessarily outlive the static lifetime

after

error: lifetime may not live long enough
  --> $DIR/type-checking-test-4.rs:20:13
   |
LL | fn test_wrong1<'a>(x: &dyn Foo<'static>, y: &'a u32) {
   |                -- lifetime `'a` defined here
LL |     let _ = x as &dyn Bar<'static, 'a>; // Error
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`

Being able to compare the expected and found types in full make it clear what's wrong.

[compiler-errors]

I looked into this one. Seems like there's not really a good way of getting a TypeTrace to find out what subtyping relation caused 'a: 'static to be required...

All we have a really bare struct ConstraintCategory that characterizes the region constraint. That's where we get the wording type annotation requires that [...] -- maybe we could make ConstraintCategory carry more info?