Fix #3300: Add check for accessibility label for activities

[Sparsh1212]

Explanation

Fixes #3300: Add check for accessibility labels for activities

The script parses the AndroidManifest.xml file of the app layer to ensure that the activity elements are defined with accessibility labels.

Note: The Activities listed in the ACCESSIBILITY_LABEL_CHECK_EXEMPTIONS_LIST will be skipped for this check, and currently, all the activities which were failing this check, have been added to this list so that the workflow doesn't fail.
We can remove any Activity from the exemption list, where we think that we can't go without a label for that Activity, or if a label is added for that Activity.

To run the script, use:

bazel run //scripts:accessibility_label_check -- $(pwd) app/src/main/AndroidManifest.xml

For testing the script, automated tests have been added.
To execute the tests, use:

bazel test //scripts:AccessibilityLabelCheckTest

Note: We are generating the test assets dynamically at the time of executing them. The test assets are automatically deleted when the test finishes.

SS when the CI check fails:

Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• The PR explanation includes the words "Fixes #bugnum: ..." (or "Fixes part of #bugnum" if the PR only partially fixes an issue).
• The PR follows the style guide.
• The PR does not contain any unnecessary auto-generated code from Android Studio.
• The PR is made from a branch that's not called "develop".
• The PR is made from a branch that is up-to-date with "develop".
• The PR's branch is based on "develop" and not on any other branch.
• The PR is assigned to an appropriate reviewer in both the Assignees and the Reviewers sections.

[Sparsh1212]

@BenHenning

• All comments addressed
• Migrated multiple exemption protos to share a single proto file and library
• Added a check for redundant exemptions
• Added tests for redundant exemptions

[BenHenning]

Thanks @Sparsh1212. Just had 2 comments, otherwise this LGTM.

[BenHenning]

Marking as requested to avoid this PR being accidentally merged before the last 2 comments are resolved.

[Sparsh1212]

@BenHenning Thanks!
Changes done. PTAL.

[BenHenning]

Thanks @Sparsh1212! LGTM.