Do not display popup icons when a popup is launched on page leave

[MortimerGoro]

Fixes #3250

I checked we match the Firefox Desktop behavior:

• Open http://popuptest.com/popuptest2.html
• Navigate to other place. Popup website triggers another popup on page leave.
• The popup is rejected and the notification/icon are not visible in the awesome bar

[bluemarvin]

Seems to not work with the back button. STR:

1. adb shell am start -a android.intent.action.VIEW -d http://www.popuptest.com/ org.mozilla.vrbrowser/.VRBrowserActivity
2. Click on Come & Go Test
3. Wait for page to be done
4. Press back button

Actual:
Nav Bar show a popup was blocked

Expected:
Nav Bar should not show a popup was blocked.

[keianhzo]

@MortimerGoro It still happens whenever you navigate to another page in the same host probably because we are delaying the state updates.
We can probably remove the postDelayed code (I think we just inherited from the previous implementation) from here:

FirefoxReality/app/src/common/shared/org/mozilla/vrbrowser/browser/PromptDelegate.java

Lines 254 to 263 in 12726e0

	mAttachedWindow.postDelayed(() -> {
	result.complete(popupPrompt.confirm(AllowOrDeny.ALLOW));
	session.setPopUpState(SessionState.POPUP_ALLOWED);
	}, 500);
	} else {
	mAttachedWindow.postDelayed(() -> {
	result.complete(popupPrompt.confirm(AllowOrDeny.DENY));
	session.setPopUpState(SessionState.POPUP_BLOCKED);
	}, 500);

and that would fix it and we wouldn't need the host check.