Fix #3291: Add check for XML syntax validation

[Sparsh1212]

Explanation

Fixes #3291: Add check for XML syntac validation

The script traverses different layers of the codebase to check for the syntax correctness of XML files
To run the script, use:

bazel run //scripts:xml_syntax_check -- $(pwd)

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

bazel test //scripts/src/javatests/org/oppia/android/scripts/xml:XmlSyntaxCheckTest

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

Blocked on: #3340

Screenshot of new tests passing locally:

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.

[anandwana001]

Thanks @Sparsh1212

Same comment from the previous PR review, for script kt file and test file.

[anandwana001]

data domain doesn't have any res file, utility does file dimen and string XML file if we are checking that else no needed, we can keep the check only for app module.

[Sparsh1212]

Yes! they don't have any res files, but my only concern was that these layers do have the AndroidManifest.xml file present, so I thought of including them too in the XML syntax check.
WDYT?

[anandwana001]

Looking for @BenHenning thoughts on this

[BenHenning]

Hmm. I just left a comment in #3340 about passing in the root directory and just recursing among that. If we validate all XML files then this slight oddity is less noticeable (since we do ultimately want all XML files to be valid). Would that mitigate the concern here?

[Sparsh1212]

Done.

[BenHenning]

Thanks @Sparsh1212! Same as #3340. This is effectively 'LGTM' with one more comment to resolve. Please resolve that & assign back once all CI tests are passing in this PR.

[BenHenning]

Thanks @Sparsh1212! LGTM, but waiting to approve until #3340 is merged. Also, per our discussion I'm cancelling the workflows for this & the next PR since that will relieve pressure on the CI system and once you merge #3340 into develop and update these PRs they should have much fewer tests to run..

[BenHenning]

Thanks @Sparsh1212! CI is green so going ahead and merging this.