Contact Form Block: Fix Missing Button Color Attributes

[Copons]

Changes proposed in this Pull Request:

The Contact Form block was missing the textButtonColor and backgroundButtonColor attributes, necessary to make it work with the SubmitButton shared component.
This practically means that, currently, you can change the colors of the Contact Form submit button, you will see the button preview updating correctly (as the colors are applied as CSS classes in the editor), but if you save the post and reload, the colors are not saved.
This only happens for "named" colors; custom colors work fine, as their attributes are not missing.

This PR adds those missing two attributes to the Contact Form block.
Also, externalizes the colourValidator utility that was being carelessly copypasted around.
I've also americanized the function name, as it's more consistent with the fact that we use color everywhere, and I'm ready to fight my British colleagues about it! 😄

Note: most changed lines here are automatic Prettier changes on the test file. 😭

Testing instructions:

• Insert a Contact Form block.
• Modify the button colors, picking from the named colors palette.
• Make sure the button updates correctly.
• Save and reload the editor.
• Make sure the button shows up with the correct colors.
• Try again with custom colors, and make sure there are no regressions.

Proposed changelog entry for your changes:

• Contact Form Block: Fix button colors not saving correctly.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello Copons! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D39932-code before merging this PR. Thank you!

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: April 7, 2020.
Scheduled code freeze: March 31, 2020

Generated by 🚫 dangerJS against 67b209e

[scruffian]

This looks good, just one nitpick about spelling!

[jeherve]

Looks good in my tests. 👍

[Copons]

r203932-wpcom

[pablinos]

Good catch! It looks like we didn't pick up the Contact Form with this change which is probably because it doesn't explicitly use the SubmitButton component.

AFAIK we shouldn't be validating the colours has hex values though. I had to remove that validation from another block as the colours can be values like light-gray coming from the theme pallette. I think this may be contributing to the problems we're seeing in the AMP change

[Copons]

@pablinos I think you're right: we should only validate custom colors (that are supposed to always be hex codes), but not named ones.
To be honest, I've done that on Contact Form, and simply updated all the other colorValidator uses with the new shared utility, without thinking much about it.

[pablinos]

Yeah looking at it again, I think I got confused by the all the colour related attributes for the Calendly block. I think there might be a couple we can deprecate now.