Rollup merge of #130234 - lukas-code:ptr-cast-errors, r=WaffleLapkin

improve compile errors for invalid ptr-to-ptr casts with trait objects

This is a follow-up to rust-lang/rust#120248 to improve some of its error messages.

1. Make the borrowcheck error for "type annotation requires that x must outlive y" actually point at the type annotation, i.e. the type `T` in a `x as T` cast. This makes the error more consistent with other errors caused by type annotation in other places, such as
```text
error: lifetime may not live long enough
 --> src/lib.rs:4:12
  |
3 | fn bar(a: &i32) {
  |           - let's call the lifetime of this reference `'1`
4 |     let b: &'static i32 = a;
  |            ^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'static`
```

2. Don't say "cast" when we actually mean "coercion" and give borrowcheck errors from actual casts (which is currently just the check added in rust-lang/rust#120248) a higher priority than ones from coercions. This can improve the errors for ptr-to-ptr cast between trait objects because they are are lowered as an upcast "unsizing" coercion if possible (which may be the identity upcast) followed by the actual cast.

3. Bring back the old "casting X as Y is invalid" message for type mismatch in the principals and reword the "vtable kinds may not match" message to more accurately describe the pointer metadata and not refer to "vtables" if the metadata is unknown.

fixes rust-lang/rust#130030

r? `@WaffleLapkin` but feel free to reassign

Author: tgross35

tests/fail/dyn-upcast-trait-mismatch.stderr

@@ -2,7 +2,7 @@ error: Undefined Behavior: using vtable for `Baz` but `Bar` was expected
   --> tests/fail/dyn-upcast-trait-mismatch.rs:LL:CC
    |
 LL |         let _err = baz_fake as *const dyn Foo;
-   |                    ^^^^^^^^ using vtable for `Baz` but `Bar` was expected
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^ using vtable for `Baz` but `Bar` was expected
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information