Rollup merge of #69745 - estebank:predicate-obligations-3, r=nikomatsakis,eddyb

Use `PredicateObligation`s instead of `Predicate`s

Keep more information about trait binding failures. Use more specific spans by pointing at bindings that introduce obligations.

Subset of #69709.

r? @eddyb

src/test/ui/error-codes/E0271.stderr

@@ -2,7 +2,7 @@ error[E0271]: type mismatch resolving `<i8 as Trait>::AssociatedType == u32`
   --> $DIR/E0271.rs:10:5
    |
 LL | fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
-   |    ---                         ------------------ required by this bound in `foo`
+   |                                ------------------ required by this bound in `foo`
 ...
 LL |     foo(3_i8);
    |     ^^^ expected `u32`, found `&str`

src/test/ui/error-codes/E0275.stderr

@@ -2,7 +2,7 @@ error[E0275]: overflow evaluating the requirement `Bar<Bar<Bar<Bar<Bar<Bar<Bar<B
   --> $DIR/E0275.rs:5:33
    |
 LL | trait Foo {}
-   | --------- required by `Foo`
+   | --------- required by this bound in `Foo`
 ...
 LL | impl<T> Foo for T where Bar<T>: Foo {}
    |                                 ^^^

src/test/ui/error-codes/E0277-2.stderr

@@ -2,7 +2,7 @@ error[E0277]: `*const u8` cannot be sent between threads safely
   --> $DIR/E0277-2.rs:16:5
    |
 LL | fn is_send<T: Send>() { }
-   |    -------    ---- required by this bound in `is_send`
+   |               ---- required by this bound in `is_send`
 ...
 LL |     is_send::<Foo>();
    |     ^^^^^^^^^^^^^^ `*const u8` cannot be sent between threads safely

src/test/ui/error-codes/E0277.stderr

@@ -14,7 +14,7 @@ error[E0277]: the trait bound `i32: Foo` is not satisfied
   --> $DIR/E0277.rs:17:15
    |
 LL | fn some_func<T: Foo>(foo: T) {
-   |    ---------    --- required by this bound in `some_func`
+   |                 --- required by this bound in `some_func`
 ...
 LL |     some_func(5i32);
    |               ^^^^ the trait `Foo` is not implemented for `i32`