Rollup merge of #70457 - Centril:non-exhaustive-scrutinee-type, r=estebank

non-exhastive diagnostic: add note re. scrutinee type

This fixes https://github.com/rust-lang/rust/issues/67259 by adding a note:
```
    = note: the matched value is of type &[i32]
```
to non-exhaustive pattern matching errors.

r? @varkor @estebank

src/test/ui/error-codes/E0004-2.stderr

@@ -13,6 +13,7 @@ LL |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
    |     ---- not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   = note: the matched value is of type `std::option::Option<i32>`
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0004.stderr

@@ -12,6 +12,7 @@ LL |       match x {
    |             ^ pattern `HastaLaVistaBaby` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   = note: the matched value is of type `Terminator`
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0005.stderr

@@ -11,6 +11,7 @@ LL |     None,
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: the matched value is of type `std::option::Option<i32>`
 help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     if let Some(y) = x { /* */ }

src/test/ui/error-codes/E0297.stderr

@@ -8,6 +8,8 @@ LL |     for Some(x) in xs {}
    |
 LL |     None,
    |     ---- not covered
+   |
+   = note: the matched value is of type `std::option::Option<i32>`
 
 error: aborting due to previous error