Refactor search term tab grouping logic to rely on middleware

[csadilek]

In mozilla-mobile/android-components#11272 we have added tab partitions/groups to BrowserState which will make it easier to represent the state of tab groups, as opposed to inferring those groups on demand.

We will need to add a middleware to Fenix that manages the corresponding tab groups. A draft of what this would look like can be found in the RFC.

The middleware will have to react to:

• SetHistoryMetadataKeyAction to add a tab to the group or remove it in case the search terms got cleared
• DisbandSearchGroupAction to remove the entire group
• RestoreCompleteAction to update the groups based on all restored tabs after startup
• RestoreTabAction to put a tab back in its group e.g. when it was deleted and undo was triggered

┆Issue is synchronized with this Jira Task

[csadilek]

/cc @rocketsroger @Amejia481 @jonalmeida