Color Palette support setup with single array argument (backwards compatible)

[webmandesign]

Description

Allowing editor-color-palette theme support setup with a single array of colors parameter/argument. This way only one argument is passed to add_theme_support( 'editor-color-palette', $arg ) instead of multiple arguments for each color.

This code is backwards compatible with current implementation (colors are passed as multiple parameters/arguments).

Fising issue #6425

[webmandesign]

This code has been discussed in #6437 that was closed due to messy rebase.

[chrisvanpatten]

Would it be possible to refresh this and look at landing it it with 3.2? Happy to do it myself if you aren't available @webmandesign.

(cc @jorgefilipecosta, since you reviewed the original PR!)

[webmandesign]

@chrisvanpatten Thanks, I'm OK doing it myself.
I've already done a rebase of my original/previous PR for the issue and it seemed to be very messy (at least from my point of view). As this PR is behind master again (more than 180 commits behind), I will create a new one, so the code will be cleaner. I'm on it ;)

[webmandesign]

@chrisvanpatten @jorgefilipecosta
I've created a new PR with updated code matching current master. #7619