Fix part of #2613: A11y Onboarding Flow

[yashraj-01]

Explanation

Fixes part of #2613 : The bottom dots now read as progress like "Slide n of 4" where n is the slide number.

Screenshot of tests passing

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.

[yashraj-01]

@rt4914 PTAL. If the approach is correct then I'll write tests for it as well. Thanks.

[anandwana001]

@yashraj-iitr Please follow the guide - https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section

[yashraj-01]

@yashraj-iitr Please follow the guide - https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section

Apologies. I forgot. Thanks for reminding.

[rt4914]

Please add tests to check that the content description is correctly set.

[yashraj-01]

I have written tests to check that the content description is correctly set. @rt4914 PTAL.

[rt4914]

@yashraj-iitr Suggested changes.

[yashraj-01]

I have addressed all the comments. @rt4914 PTAL.

[rt4914]

@yashraj-iitr I have replied to one open comment. PTAL

[rt4914]

LGTM. Thanks.