Merge xml

[aadityaguptaa]

Fixes #3580

merges the 4 xmls of topic_lessons_fragment into single xml file

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.
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For UI-specific PRs only

If your PR includes UI-related changes, then:

• Add screenshots for portrait/landscape for both a tablet & phone of the before & after UI changes

--Before ss of the Portrait mode mobile

--After ss of the Portrait mode mobile

--Before ss of the landscape mode mobile

--After ss of the landscape mode mobile

[rt4914]

LGTM, thanks.