Remember scroll position when saving sessions

[severinrudie]

Depends on mozilla-mobile/android-components#2700

Why/User Benefit/User Problem

It is common for users to read part of an article, close their phones, and return to finish later. Their session is currently saved when they do so, but their scroll position is not.

[Vesta]
As a user, I want to be able to close the browser, and when I come back to my last session, start reading where I left off. This is key to aligning to our vision of building a browser that is fast by design.

What / Requirements

Scroll position should be saved whenever a session is persisted, and restored when it is reopened.

Acceptance Criteria (how do I know when I’m done?)

I can re-open a session to where I left off in the page.

┆Issue is synchronized with this Jira Task

[vesta0]

Needs an A-C issue and investigation into whether GV work is required @pocmo @boek

[pocmo]

Removed a bunch of labels (a-c, Needs GV work, blocked). This has been fixed in GeckoView and uplifted. It's working in RB.

[vesta0]

Thank you @pocmo I believe it's also working in Fenix :)

[lobontiumira]

Verified as fixed on the latest build 1.0.1923 (#11550608), with Huawei MediaPad M2 (Android 5.1.1), Sony Xperia Z5 Premium (Android 7.1.1), and OnePlus 5T (Android 9).