Sort invitations by date of invite event

Currently the invitations are sorted by date of latest activity (the default sorting of the SDK), which is not correct and may lead to random ordering of invitation

This last activity time should be set to the date of the invite event for room in invitation state.

The code to update is here https://github.com/vector-im/element-android/blob/main/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/summary/RoomSummaryUpdater.kt#L134

For invites `getLatestPreviewableEvent` should not be used to set `roomSummaryEntity.lastActivityTime` but rather the date of the invite event.

This change should require an initial sync (or a database migratrion), but this is OK, let's just update the RoomSummaryUpdater.