Do not suggest introducing lifetime in impl assoc type

```
error[E0261]: use of undeclared lifetime name `'a`
  --> $DIR/missing-lifetime-in-assoc-type-2.rs:7:57
   |
LL | impl IntoIterator for &S {
   |     - help: consider introducing lifetime `'a` here: `<'a>`
...
LL |     type IntoIter = std::collections::btree_map::Values<'a, i32, T>;
   |                                                         ^^ undeclared lifetime
```

```
error[E0106]: missing lifetime specifier
  --> $DIR/issue-74918-missing-lifetime.rs:9:30
   |
LL |     type Item = IteratorChunk<T, S>;
   |                              ^ expected named lifetime parameter
   |
help: consider introducing a named lifetime parameter
   |
LL ~ impl<'a, T, S: Iterator<Item = T>> Iterator for ChunkingIterator<T, S> {
LL ~     type Item = IteratorChunk<'a, T, S>;
   |
```

Author: estebank

compiler/rustc_resolve/src/late.rs

@@ -378,6 +378,7 @@ enum LifetimeBinderKind {
     Function,
     Closure,
     ImplBlock,
+    ImplAssocType,
 }
 
 impl LifetimeBinderKind {
@@ -388,6 +389,7 @@ impl LifetimeBinderKind {
             PolyTrait => "bound",
             WhereBound => "bound",
             Item | ConstItem => "item",
+            ImplAssocType => "associated type",
             ImplBlock => "impl block",
             Function => "function",
             Closure => "closure",
@@ -3398,7 +3400,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                     &generics.params,
                     RibKind::AssocItem,
                     item.id,
-                    LifetimeBinderKind::Item,
+                    LifetimeBinderKind::ImplAssocType,
                     generics.span,
                     |this| {
                         this.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -3178,6 +3178,9 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     {
                         continue;
                     }
+                    if let LifetimeBinderKind::ImplAssocType = kind {
+                        continue;
+                    }
 
                     if !span.can_be_used_for_suggestions()
                         && suggest_note

tests/ui/lifetimes/missing-lifetime-in-assoc-type-2.stderr

@@ -14,10 +14,6 @@ LL |     type IntoIter = std::collections::btree_map::Values<'a, i32, T>;
    |
 help: consider introducing lifetime `'a` here
    |
-LL |     type IntoIter<'a> = std::collections::btree_map::Values<'a, i32, T>;
-   |                  ++++
-help: consider introducing lifetime `'a` here
-   |
 LL | impl<'a> IntoIterator for &S {
    |     ++++
 

tests/ui/lifetimes/missing-lifetime-in-assoc-type-3.stderr

@@ -14,8 +14,11 @@ LL |     type IntoIter = std::collections::btree_map::Values<i32, T>;
    |
 help: consider introducing a named lifetime parameter
    |
-LL |     type IntoIter<'a> = std::collections::btree_map::Values<'a, i32, T>;
-   |                  ++++                                       +++
+LL ~ impl<'a> IntoIterator for &S {
+LL |     type Item = &T;
+LL |
+LL ~     type IntoIter = std::collections::btree_map::Values<'a, i32, T>;
+   |
 
 error: aborting due to 2 previous errors
 

tests/ui/lifetimes/missing-lifetime-in-assoc-type-5.stderr

@@ -20,8 +20,9 @@ LL | impl<'a> IntoIterator for &'_ S {
    |
 help: consider using the named lifetime here instead of an implict lifetime
    |
-LL | impl<'a> IntoIterator for &'a S {
-   |                            ~~
+LL - impl<'a> IntoIterator for &'_ S {
+LL + impl<'a> IntoIterator for &'a S {
+   |
 
 error: aborting due to 2 previous errors
 

tests/ui/mismatched_types/issue-74918-missing-lifetime.stderr

@@ -6,8 +6,9 @@ LL |     type Item = IteratorChunk<T, S>;
    |
 help: consider introducing a named lifetime parameter
    |
-LL |     type Item<'a> = IteratorChunk<'a, T, S>;
-   |              ++++                 +++
+LL ~ impl<'a, T, S: Iterator<Item = T>> Iterator for ChunkingIterator<T, S> {
+LL ~     type Item = IteratorChunk<'a, T, S>;
+   |
 
 error: aborting due to 1 previous error
 

tests/ui/nll/user-annotations/region-error-ice-109072.stderr

@@ -17,10 +17,6 @@ LL |     type T = &'missing ();
    |
 help: consider introducing lifetime `'missing` here
    |
-LL |     type T<'missing> = &'missing ();
-   |           ++++++++++
-help: consider introducing lifetime `'missing` here
-   |
 LL | impl<'missing> Lt<'missing> for () {
    |     ++++++++++