Add progressConverter property to OverscrollBuilder (1/2)

The progressConverter is a function allows you to specify the progress
value used by the Overscroll DSL during an overscroll.

The function takes a linear overscroll progress value ranging from 0 to
 +/- infinity and outputs the desired **overscroll progress value**.

When the progress value is:
- 0, the user is not overscrolling.
- 1, the user overscrolled by exactly the scene distance.
- Greater than 1, the user overscrolled more than the scene distance.

Test: atest ElementTest
Bug: 291053278
Flag: com.android.systemui.scene_container
Change-Id: I38bfb417e4a97a29c351192c8196c741f5efbb44