Add redundancy for app module ownership

[BenHenning]

Explanation

Updates codeowners for non-XML app module files to ensure there's ownership redundancy (to reduce codereview load on @rt4914 & as part of his transition plan).

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

N/A -- This is nly changing codeowners.

[BenHenning]

@rt4914 @seanlip PTAL.

[rt4914]

LGTM. Thanks a lot @BenHenning

[oppiabot]

Unassigning @rt4914 since they have already approved the PR.

[seanlip]

@BenHenning FYI automated checks are failing.

[oppiabot]

Hi @BenHenning, this PR is ready to be merged. Please address any remaining comments prior to merging, and feel free to merge this PR once the CI checks pass and you're happy with it. Thanks!

[BenHenning]

Thanks both!