Fix onboarding library integration

[Gudahtt]

Fixes: #9792

Explanation:

The bug with our onboarding library integration was introduced in #8873 because of a change in when completeOnboarding was called. We hadn't realized at the time that the onboarding integration relied upon the onboarding completing event to know when the onboarding state should be cleared. Because onboarding is now marked as completed earlier, the state was cleared just as it was intended to be used.

The onboarding completed event has been moved back to where it was before: after the user exits the "end of flow" page.

The original problem that #8873 was addressing was a routing issue, where the user would be redirected back to the seed phrase confirmation page despite already having confirmed their seed phrase. This was fixed in a different way here, by updating the routing in the first time flow switch to skip straight to the end of flow page if the seed phrase has already been confirmed.

This does involve one user-facing change in behavior; if the user opens any MetaMask UI before navigating away from the end-of-flow screen, they will still be considered mid-onboarding so it'll redirect to the end-of-flow screen. But we do mark onboarding as completed if the user closes the tab/window while on the end of flow screen, which was another goal of #8873.

Manual testing steps:

To test that the onboarding integration works:

• Open a browser without MetaMask installed
• Navigate to https://metamask.github.io/test-dapp/
• Press the "CLICK HERE TO INSTALL METAMASK" button
• Install MetaMask
• Proceed through onboarding to the last page
• See that the message "All Done" will close this tab and direct back to https://metamask.github.io/test-dapp/ is shown below the "All done" button

To test that the user is redirected back to the end-of-flow page if the user opens a tab while the end of flow page is open:

• Install MetaMask
• Proceed through onboarding to the last page
• Open the MetaMask popup while on the last page of onboarding
• See that a new tab is opened, which navigates to the last page of onboarding

To test that onboarding is marked as completed when the end of flow page is closed:

• Install MetaMask
• Proceed through onboarding to the last page
• Close the tab
• Open the MetaMask popup, and see that the home screen is shown

[metamaskbot]

Builds ready [6985c67]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (474 ± 39 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	35	105	52	20	9
		domContentLoaded	374	755	472	82	39
		load	376	757	474	82	39
		domInteractive	374	754	472	82	39

[Gudahtt]

This depends upon #9830

[metamaskbot]

Builds ready [6e123d1]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (374 ± 48 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	29	85	40	11	5
		domContentLoaded	254	620	373	99	48
		load	255	621	374	100	48
		domInteractive	254	619	372	99	48

[darkwing]

All flows worked exactly as described!