Migrates the component to spectrum two.
- Theme files are removed, and their custom properties integrated into
  the main index.css.
- Renames misspelled mod custom property (noted in docs)
- Simplifies background color styles by changing a single custom
  property per variant, as done on other components.

Adjust some spacings to match the Spectrum 2 spec spacing.
And renames some mods so they are more consistent with current naming
conventions, and their purpose is more clear.

=== Update spacing to match the Spectrum 2 spec ===

One issue with the S1 version was that there was too much space between
the text and the button, when the button wrapped to the next line. And
there was a different token defined for the space from the bottom edge
to the text, and vertically between the button and the text.

This helps resolve this by moving some of the spacing to padding on the
AlertBanner-body, and subtracting this value from some of the other
custom properties. Along with using both column-gap and row-gap
properties.

=== adjust storybook template spacing and decorator ===

Improves spacing in Storybook template, especially the Chromatic only
template. Decorator and wrapper styles are modeled after those used in
Action button, so they look more similar. Previously the layout was a
little cramped and the "detail" elements were missing their margins
because they were display inline.

Creates a custom MDX docs page in Storybook for the Alert banner
component. And reworks the stories and chromatic-only templates a little
to facilitate and increase coverage.

Includes Storybook VRT coverage for the max width changes in PR #2762 .
Tests the display of the alert banner when in a container larger than
and smaller than its max-inline-size.

- Add stylelint disable line comments for some false positives caught by
  the linter.
- Re-generate mods file