First pass attempt at creating a block support for adding a width selector with options for
25, 50, 75, 100 percent width. It is based off the work to add a block support for border
radius.

The intention is to extend this to include custom percentage widths and px support with a
slider in the editor for custom sizing (see Search bar for an example).

When a custom width is selected apply the 'custom-width' className to the block.
This is used to key off of for additional block-specific CSS; for example the
Button block needs to set its inner component to 100% width for the styling to
work correctly.

Nesting width into a dimension setting allows for the addition of related
settings (height etc) in the future.

Adding a block support using CSS variables to the Button block
causes the inline style to be added to the button's wrapper div as
well as the inner anchor tag. This causes Block Invalidation
errors for existing posts, as well as for any patterns that use
the Button block.

These errors are resolved with a deprecation that omits the block
support. Once opened in the block editor they migrate cleanly.

Fix up an incorrectly applied rebase.

The use of `useBlockProps` in the Button block was causing all of
the block's style attributes to be applied to the button's
wrapper div, including color props that were previously applied
only to the inner anchor tag. When a Button has both a custom
background color and a border radius, this causes and issue where
the background color (applied to the wrapper) exceeds the lines
of the border (applied to the inner anchor tag).

This commit removes style attributes related to the color props
from the blockProps before they are applied to the wrapper. This
also resolves the block invalidation errors that were previously
addressed by a block deprecation, so the deprecation is no longer
necessary and is also removed in this commit.

Some docstrings still referred to the block support as just width
support, and needed to be updated after refactoring into a larger
dimensions feature.

Properly register the block support and apply the CSS variable inline
styles for dynamic blocks that are rendered in PHP.

Because block supports implemented with CSS variables add styling to
the outermost element of a block, this commit updates the Button
block to expect styling to be applied at this level, rather than
directly setting it on the inner component. This is accomplished by:

1. Updates the CSS so that the inner button will always inherit
color, background-color, and border-radius styling that was applied
inline to its wrapper. This only happens when a user has selected
an option from a block support, so we can reliably override any other
styling applied by defaults or the theme.

2. Adds a deprecation for the Button block since styling is now
applied differently.

3. Removes the block-specific implementation of Color settings and
instead applies the color block support.

4. Temporarily manually applies the border-radius to the wrapper.
There is a PR for a border radius block support, which can be used to
replace this.