Rollup merge of #130116 - veera-sivarajan:freeze-suggestions, r=chenyukang

Implement a Method to Seal `DiagInner`'s Suggestions

This PR adds a method on `DiagInner` called `.seal_suggestions()` to prevent new suggestions from being added while preserving existing suggestions.

This is useful because currently there is no way to prevent new suggestions from being added to a diagnostic. `.disable_suggestions()` is the closest but it gets rid of all suggestions before and after the call.

Therefore, `.seal_suggestions()` can be used when, for example, misspelled keyword is detected and reported. In such cases, we may want to prevent other suggestions from being added to the diagnostic, as they would likely be meaningless once the misspelled keyword is identified. For context: https://github.com/rust-lang/rust/pull/129899#discussion_r1741307132

To store an additional state, the type of the `suggestions` field in `DiagInner` was changed into a three variant enum. While this change affects files across different crates, care was taken to preserve the existing code's semantics. This is validated by the fact that all UI tests pass without any modifications.

r? chenyukang

tests/ui/parser/issues/issue-70549-resolve-after-recovered-self-ctor.stderr

@@ -14,10 +14,6 @@ help: there is a keyword `mut` with a similar name
    |
 LL |     fn foo(&mut Self) {}
    |             ~~~
-help: declare the type after the parameter binding
-   |
-LL |     fn foo(<identifier>: <type>) {}
-   |            ~~~~~~~~~~~~~~~~~~~~
 
 error: unexpected lifetime `'static` in pattern
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:8:13
@@ -47,10 +43,6 @@ help: there is a keyword `mut` with a similar name
    |
 LL |     fn bar(&'static mut Self) {}
    |                     ~~~
-help: declare the type after the parameter binding
-   |
-LL |     fn bar(<identifier>: <type>) {}
-   |            ~~~~~~~~~~~~~~~~~~~~
 
 error: expected one of `:`, `@`, or `|`, found keyword `Self`
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:14:17

tests/ui/parser/misspelled-keywords/impl-trait.stderr

@@ -8,10 +8,6 @@ help: there is a keyword `impl` with a similar name
    |
 LL | fn code<T: impl Debug>() -> u8 {}
    |            ~~~~
-help: you might have meant to end the type parameters here
-   |
-LL | fn code<T: impll> Debug>() -> u8 {}
-   |                 +
 
 error: aborting due to 1 previous error
 

tests/ui/parser/misspelled-keywords/ref.stderr

@@ -8,10 +8,6 @@ help: there is a keyword `ref` with a similar name
    |
 LL |         Some(ref list) => println!("{list:?}"),
    |              ~~~
-help: missing `,`
-   |
-LL |         Some(refe, list) => println!("{list:?}"),
-   |                  +
 
 error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 1 field
   --> $DIR/ref.rs:4:14