Use our own JoinRule type which doesn't include the reserved .private case. (#5056)

* Stop using Rust's JoinRule.private in mocks.

It isn't used anywhere else (see MSC4413 for more context).

* Use our own JoinRule (and AllowRule) types.

* Update ElementX/Sources/Services/Room/JoinRule.swift

Co-authored-by: Stefan Ceriu <stefan.ceriu@gmail.com>

---------

Co-authored-by: Stefan Ceriu <stefan.ceriu@gmail.com>

ElementX/Sources/Screens/Spaces/Common/SpaceHeaderView.swift

@@ -141,7 +141,7 @@ struct SpaceHeaderView_Previews: PreviewProvider, TestablePreview {
                                           "Interdum mauris ultrices tincidunt proin morbi erat aenean risus nibh.",
                                           "Diam amet sit fermentum vulputate faucibus."].joined(separator: " "),
                                   canonicalAlias: "#subspace:matrix.org",
-                                  joinRule: .knockRestricted(rules: [.roomMembership(roomId: "")]))
+                                  joinRule: .knockRestricted(rules: [.roomMembership(roomID: "")]))
         ]
     }
 }