ONLY merge this after Part 1 has been merged! (Derivative branch)

Fixes #17253 partially. (Sub-ticket of #17246)

To Test:

• AddCategoryFragment.java:

  1. Have a site with a post.
  2. Navigate to "My Site" and click on "Posts" to see all your posts. Open any post in edit mode.
  3. Click on dropdown button on top-left.
  4. Click "Post settings".
  5. Select/Open "Categories".
  6. Click on "+" symbol on top left.
  7. A dialog should open without errors.

• CollapseFullScreenDialogFragment.java:

  1. Navigate to "Reader" tab.
  2. On any post, click on "Comment" to open comments.
  3. On the bottom of the screen, you will have the text field to reply. Beside that, you will have an "Arrow up" button. Click it.
  4. This is our full screen dialog that got changed. It should work as expected.

• SignupEpilogueFragment.java:

  1. Just follow the signup flow till you reach a form where you have to fill your name, display name and password.
  2. This is hard to test (and I need help here). The changes in this file are minute and are certainly not going to break anything afaik.

• SitePickerActivity.java:

  1. Navigate to "My Site" tab.
  2. Click on "Add Site" button if you have no sites else, click on current opened site's title on top of the page (with an arrow).
  3. You will have "Choose site" screen infront of you.
  4. Click on "+" button on top right. (on Action bar)
  5. Dialog should work as expected.

• PersonDetailFragment.java:

  1. Have at least one site.
  2. Navigate to "My Site" tab.
  3. Click on "More".
  4. Click on "People"
  5. Click on any person.
  6. A detailed view of the person should pop up as expected.

Regression Notes

1. Potential unintended areas of impact
   Mostly none because the newer API's are a direct replacement.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manual Testing

3. What automated tests I added (or what prevented me from doing so)
   None

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

UI Changes testing checklist:

• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• Talkback.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• Large and small screen sizes. (Tablet and smaller phones)
• Multi-tasking: Split screen and Pop-up view. (Android 10 or higher)