Show scrutinee expr type for struct fields.

TODO: The type is wrong and will be fixed in later commits.

src/test/ui/pattern/pat-struct-field-expr-has-type.rs

@@ -0,0 +1,9 @@
+struct S {
+    f: u8,
+}
+
+fn main() {
+    match (S { f: 42 }) {
+        S { f: Ok(_) } => {} //~ ERROR mismatched types
+    }
+}

src/test/ui/pattern/pat-struct-field-expr-has-type.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/pat-struct-field-expr-has-type.rs:7:16
+   |
+LL |     match (S { f: 42 }) {
+   |           ------------- this expression has type `u8`
+LL |         S { f: Ok(_) } => {}
+   |                ^^^^^ expected `u8`, found enum `std::result::Result`
+   |
+   = note: expected type `u8`
+              found enum `std::result::Result<_, _>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.