parse: use parse_item_common in parse_assoc_item_.

src/test/ui/issues/issue-58856-1.stderr

@@ -9,8 +9,14 @@ LL |     fn b(self>
 error: expected `;` or `{`, found `>`
   --> $DIR/issue-58856-1.rs:3:14
    |
+LL | impl A {
+   |        - while parsing this item list starting here
+LL |
 LL |     fn b(self>
    |              ^ expected `;` or `{`
+...
+LL | }
+   | - the item list ends here
 
 error[E0412]: cannot find type `A` in this scope
   --> $DIR/issue-58856-1.rs:1:6

src/test/ui/issues/issue-58856-2.rs

@@ -9,6 +9,6 @@ impl Howness for () {
         Empty
     }
 }
-//~^ ERROR expected one of `async`, `const`, `crate`, `default`, `extern`, `fn`,
+//~^ ERROR non-item in item list
 
 fn main() {}

src/test/ui/issues/issue-58856-2.stderr

@@ -7,13 +7,17 @@ LL |     fn how_are_you(&self -> Empty {
    |                   |     help: `)` may belong here
    |                   unclosed delimiter
 
-error: expected one of `async`, `const`, `crate`, `default`, `extern`, `fn`, `pub`, `static`, `type`, `unsafe`, `}`, or identifier, found `)`
+error: non-item in item list
   --> $DIR/issue-58856-2.rs:11:1
    |
-LL |     }
-   |      - expected one of 12 possible tokens
+LL | impl Howness for () {
+   |                     - item list starts here
+...
 LL | }
-   | ^ unexpected token
+   | ^
+   | |
+   | non-item starts here
+   | item list ends here
 
 error[E0407]: method `how_are_you` is not a member of trait `Howness`
   --> $DIR/issue-58856-2.rs:6:5

src/test/ui/issues/issue-60075.rs

@@ -4,7 +4,8 @@ trait T {
     fn qux() -> Option<usize> {
         let _ = if true {
         });
-//~^ ERROR expected one of `async`
-//~| ERROR expected one of `.`, `;`, `?`, `else`, or an operator, found `}`
+//~^ ERROR non-item in item list
+//~| ERROR mismatched closing delimiter: `)`
+//~| ERROR expected one of `.`, `;`
         Some(4)
     }

src/test/ui/issues/issue-60075.stderr

@@ -4,14 +4,26 @@ error: expected one of `.`, `;`, `?`, `else`, or an operator, found `}`
 LL |         });
    |          ^ expected one of `.`, `;`, `?`, `else`, or an operator
 
-error: expected one of `async`, `const`, `crate`, `default`, `extern`, `fn`, `pub`, `static`, `type`, `unsafe`, `}`, or identifier, found `;`
+error: non-item in item list
   --> $DIR/issue-60075.rs:6:11
    |
+LL | trait T {
+   |         - item list starts here
+...
+LL |         });
+   |           ^ non-item starts here
+...
+LL |     }
+   |     - item list ends here
+
+error: mismatched closing delimiter: `)`
+  --> $DIR/issue-60075.rs:6:10
+   |
 LL |     fn qux() -> Option<usize> {
    |                               - unclosed delimiter
 LL |         let _ = if true {
 LL |         });
-   |           ^ help: `}` may belong here
+   |          ^ mismatched closing delimiter
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors