Show a prompt to reinvite other party in a DM

If you are looking at a DM where the other party has left then
when you focus the composer for the first time we'll show a
dialog asking if you want to reinvite the other party.

Closes #590

tests/uitests/src/test/snapshots/images/io.element.android.tests.uitests_ScreenshotTest_preview_tests[io.element.android.features.messages.impl_null_DefaultGroup_MessagesViewDarkPreview_0_null_4,NEXUS_5,1.0,en].png

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