[Bug] TabCounterToolbarButton never stops observing the SessionManager

[jonalmeida]

The TabCounterToolbarButton was copied from a-c but does not stop observing the SessionManager when the view is destroyed which may lead to memory leaking.

The fix would be to pass the view's parent so the observer can stop when the view is destroyed, or use the a-c component directly. 🙂

The code that leaks: https://github.com/mozilla-mobile/fenix/blob/master/app/src/main/java/org/mozilla/fenix/components/toolbar/TabCounterToolbarButton.kt#L27

The a-c implementation: https://github.com/mozilla-mobile/android-components/blob/master/components/feature/tabs/src/main/java/mozilla/components/feature/tabs/toolbar/TabCounterToolbarButton.kt#L28

┆Issue is synchronized with this Jira Task