Properly dispose of web ComposeWindow on removing canvas from DOM

[cedrickcooke]

Prior to this, web's ComposeWindow.dispose() function was never called. Now, dispose is called when the ComposeWindow's canvas is removed from the html document. This approach allows for proper cleanup in cases where a web SPA uses compose for some (but not all) logical pages.

Testing

Before implementing this work, I updated ComposeWindowLifecycleTest.allEvents to pass consistently. Then I implemented the disposal call, and extended the allEvents test to trigger a disposal and check the new lifecycle events.

Release Notes

Fixes - Web

• Dispose of ComposeWindow when removed from document.

[ApoloApps]

Calling dispose in beforeunload is wrong. This event can be used to show a dialog confirming if the user wants to close the tab, but the user can click cancel and tab closing will be prevented which will leave you with no content since it has been disposed

[cedrickcooke]

Good callout, I've updated things to only use the canvas removal trigger

[cedrickcooke]

Sorry for the delay on that.

In my original local testing the window was grabbing focus when launched, so the compose window was initialized in the RESUMED state. It seems like on the test runners the window isn't initially focused, so it was stuck on STARTED.

I've updated the test to send an extra focus event before the first check for RESUMED. If the window is already focused this is a no-op, and if the window is not focused this will push it into the RESUMED state. Then the test performs a full blur/focus loop as before.

[cedrickcooke]

Please forgive the force-push. This has been updated to work with the shadow root changes. While doing so, I also updated this test to use the createComposeWindow function like the other tests.