Stop using MaterialTheme in the library's code

[Nek-12]

Describe the bug
Stop using MaterialTheme because that leads to hardcoded material theme values throughout the library.
I discovered this issue while trying to override all colors and shapes of the dialogs for Material3 migration. I discovered that many usages of MaterialTheme (from material2) are found inside the library's internal code.

To Reproduce

1. Use Material3 and remove material2 AppTheme() from the composition
2. Watch your dialogs get broken without a way to override all colors.
   Example of hardcoded properties: Shapes and ":" text color and style of the Time Picker dialog.

Expected behaviour
When I provide the picker with colors, they must be actually used, not just for the sake of it.

Screenshots