Fix #3535: Merge hints_and_solution_fragment.xml into one file

[adizcode]

Explanation

Fixes #3535 by merging 4 different layout files into one

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

If your PR includes UI-related changes, then:

• Add screenshots for portrait/landscape for both a tablet & phone of the before & after UI changes
• For the screenshots above, include both English and pseudo-localized (RTL) screenshots (see RTL guide)
• Add a video showing the full UX flow with a screen reader enabled (see accessibility guide)
• Add a screenshot demonstrating that you ran affected Espresso tests locally & that they're passing

Before	After

[oppiabot]

Unassigning @vrajdesai78 since they have already approved the PR.

[oppiabot]

Assigning @rt4914 for code owner reviews. Thanks!

[rt4914]

LGTM, thanks

[oppiabot]

Unassigning @rt4914 since they have already approved the PR.