Cache findViewById calls in session control

[NotWoods]

Since we use kotlin synthetics in ViewHolders a lot, I added a helper class that implements the LayoutContainer interface. This interface lets us refer to views with their ID directly without the view. prefix, just like Activities and Fragments. Additionally, this caches the underlying findViewById calls to help with perf.

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[firefoxci-taskcluster]

No Taskcluster jobs started for this pull request

The `allowPullRequests` configuration for this repository (in `.taskcluster.yml` on the
default branch) does not allow starting tasks for this pull request.

[ekager]

I just had @liuche add you back to the org 🙈 closing + reopening to see if CI will run

[BranescuMihai]

Looks good!