Companion to #6958 (Android/Desktop). Channel-link "Share via chat"
picker showed Saved Messages, which produced `Failed reading: empty`
on tap because `*<id>` has no branch in `sendRefP`. Add `includeLocal`
flag to `filterChatsToForwardTo` (default true) and to
`ChatItemForwardingView`; `shareChannelPicker` passes false.
Bug #2 from #6958 (button on plain groups) is not present on iOS —
`GroupLinkView.swift:110` already gates by `publicGroup != nil`.