use colored backdrop for Input Screen alpha transitions on API 33+

[LukasPaczos]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1208671518894266/task/1210820490944337?focus=true

Description

Uses the backdrop API for window transitions to supply a backdrop color which is drawn below and beyond bounds of the activity to prevent the activity window fading to black during alpha transitions.

I remove the translation transition from API < 31 because it didn't run on tested devices anyway.

Additionally, I cleaned up the transition files and moved them to duckchat module, which is more appropriate as they are targeted specifically at the Input Screen transition behavior.

Steps to test this PR

• Verify the slide + fade transitions look right in light and dark mode on API >= 33
• Verify the fade transition looks right in light and dark mode on API < 33 (unchaged behavior)

UI changes (for API 33+)

Before	After

[joshliebe]

Tested on API 27 & API 36 ✅
Animation is really smooth but I think 300ms is a little too slow now, 200ms might work better.