Button improvements

[islemaster]

While working on #23625 I noticed some things I don't like about our Button component, so I'm changing them. I've also updated the storybook entry for Buttons to be more browsable.

This will cause eyes changes.

Before

(Disabled)

1. The button colors that use white lettering on bold colors can be difficult to read; the lettering is almost too fine.
2. The "disabled" styles for some button colors are surprising, and for others (especially red) indicate no difference at all.
3. A button with the disabled prop and an href prop is still a clickable link.

After

(Disabled)

1. Buttons that use white lettering also use font-weight: bold for readability.
2. All button colors have disabled styles.
3. A button with the disabled prop and an href prop does nothing when clicked.

[Erin007]

Yeah! These are so much more readable!

[islemaster]

-Josh, +Ram (DOTD) since this will cause eyes changes on the next test run after merge.