Convert @IntDefenums to normal enums where rational

[dustdfg]

What is it?

• Codebase improvement (dev facing)

Description of the changes in your PR

• Convert @IntDefenums to normal enums where rational

Reasons to not convert other @IntDef to enums:

• ...NotificationConstants.java - heavily relies on int semantics, uses int semantics for storing data, very messy, part of the player... (Just formally could be converted but it is really a mess)
• ...CollapsibleView.java - probably will be deleted in Remove file orphaned for long time #13019
• ...NotificationMode.kt- should be int to store in db. Used inside other structs so adding @TypeConverteris not applicable (?)
• ...FragmentStatePagerAdapterMenuWorkaround - external and deprecated code copied from library and edited for adding some workaround. No need to "fix"

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR. You can find more info and a video demonstration on this wiki page.

Due diligence

• I read the contribution guidelines.
• The proposed changes follow the AI policy.
• [*] I tested the changes using an emulator or a physical device.