Fix duplicate type mismatches with blocks

E.g. when there's a type mismatch on the return value of a function. To
fix this, we have to return the expected type as the type of the block
when there's a mismatch. That meant some IDE code that expected
otherwise had to be adapted, in particular the "add return type" assist.
For the "wrap in Ok/Some" quickfix, this sadly means it usually can't be applied
in all branches of an if expression at the same time anymore, because
there's a type mismatch for each branch that has the wrong type.

crates/ide_diagnostics/src/tests.rs

@@ -54,13 +54,13 @@ fn check_nth_fix(nth: usize, ra_fixture_before: &str, ra_fixture_after: &str) {
         actual
     };
 
-    assert_eq_text!(&after, &actual);
     assert!(
         fix.target.contains_inclusive(file_position.offset),
         "diagnostic fix range {:?} does not touch cursor position {:?}",
         fix.target,
         file_position.offset
     );
+    assert_eq_text!(&after, &actual);
 }
 
 /// Checks that there's a diagnostic *without* fix at `$0`.