Refactor TypeContents to be more scrutable. In particular, create coarser bits

than the current ones, which were very fine-grained.  Also, cleanly distinguish
when properties must be found in *owned* types vs *reachable* types.

Fixes #10157
Fixes #10278

src/test/compile-fail/mutable-enum-indirect.rs

@@ -0,0 +1,12 @@
+// Tests that an `&` pointer to something inherently mutable is itself
+// to be considered mutable.
+
+#[no_freeze]
+enum Foo { A }
+
+fn bar<T: Freeze>(_: T) {}
+
+fn main() {
+    let x = A;
+    bar(&x); //~ ERROR type parameter with an incompatible type
+}