[Button Block]: Add native mobile support for padding (WIP)

[stacimc]

Description

WIP to add native mobile support for button padding. For ease of testing this PR includes changes to add the block support to the Button block (from #31774)

There were a number of issues with adding native support for padding:

1. The spacing block support uses a BoxControl input to allow setting padding for individual sides of the button. This component is not supported natively.
2. Because it is possible to set different padding selections per-side on web, the native controls must also allow independently setting padding per side.
3. The existing native Button is implemented as a class component and must be refactored in order to use the existing utilities fro converting units for mobile.
4. The existing UnitControl, which I use here as a substitute for the BoxControl, seems to be lacking some native support -- specifically, the value and unit have to be handled separately. This vastly complicates the logic needed in an implementation of something like BoxControl.

This PR:

• Refactors Button into a functional component
• Pulls the controls out into a separate file
• Adds a very rough first pass at padding support

The logic in this first pass is overly complicated and essentially re-implements a small subset of the functionality of BoxControl. I think the correct approach from here is to abandon this work and focus on getting full native support for BoxControl.

Major Known Issues:

• The UI does not match web and is clunky/much too large.
• There is no support for changing all padding values at once, or just top/bottom left/right (they must be individually updated)
• Padding values are not visually correct, although the correct styles are being applied, and only bottom padding updates. When testing I found that applying a padding style to the button works, but paddingTop for instance does not. Using margin also works.
• The button loads in slowly on Android; the refactor needs to be analyzed for its effect on performance.
• Padding causes issues when width is set on the button
• The + and - controls on the UnitControl are very buggy ( eg if you click twice it goes from 1 to 11 )

How has this been tested?

Manually. Because this PR refactors the button, all functionality must be tested.

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[stacimc]

Closing this PR until BoxControl is supported natively.