fix location of variable when function definition {v => ...} is enclosed in braces

In addition to creating problems with the analysis performed by the editor integration, this was not issue a warning for unused variable:

```res
let _ = {thisGetsBrokenLoc => 4}
```

Author: cristianoc

CHANGELOG.md

@@ -49,6 +49,7 @@ These are only breaking changes for unformatted code.
 - Fix issue where the internal representation of uncurried types would leak when a non-function is applied in a curried way https://github.com/rescript-lang/rescript-compiler/pull/5892
 - In GenType, check annotations also in module types to decide whether to produce the `.gen.tsx` file https://github.com/rescript-lang/rescript-compiler/pull/5903
 - Fix some comments disappearing in array access expressions https://github.com/rescript-lang/rescript-compiler/pull/5947
+- Parser: fix location of variable when function definition `{v => ...}` is enclosed in braces https://github.com/rescript-lang/rescript-compiler/pull/5949
 
 #### :nail_care: Polish
 

res_syntax/src/res_core.ml

@@ -2933,7 +2933,7 @@ and parseBracedOrRecordExpr p =
                     attrs = [];
                     label = Asttypes.Nolabel;
                     expr = None;
-                    pat = Ast_helper.Pat.var ident;
+                    pat = Ast_helper.Pat.var ~loc:ident.loc ident;
                     pos = startPos;
                   };
               ]