Rollup merge of #77640 - ethanboxx:int_error_matching_attempt_2, r=KodrAus

Refactor IntErrorKind to avoid "underflow" terminology

This PR is a continuation of #76455

# Changes

- `Overflow` renamed to `PosOverflow` and `Underflow` renamed to `NegOverflow` after discussion in #76455
- Changed some of the parsing code to return `InvalidDigit` rather than `Empty` for strings "+" and "-". https://users.rust-lang.org/t/misleading-error-in-str-parse-for-int-types/49178
- Carry the problem `char` with the `InvalidDigit` variant.
- Necessary changes were made to the compiler as it depends on `int_error_matching`.
- Redid tests to match on specific errors.

r? ```@KodrAus```

library/core/src/lib.rs

@@ -159,6 +159,7 @@
 #![feature(slice_ptr_get)]
 #![feature(no_niche)] // rust-lang/rust#68303
 #![feature(unsafe_block_in_unsafe_fn)]
+#![feature(int_error_matching)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 #[prelude_import]