add logic for custom color boolean for borders

[n8finch]

First PR for Gutenberg, woohoo!

What?

Closes #59567

This PR fixes the disableCustomColors prop that was not being set in the BorderBoxControl element.

Why?

If the custom color setting is disabled in the theme.json the BorderBoxControl element was not picking up on that setting.

The setting was respected when picking text and background colors though, as these use the ColorPanelDropdown element.

How?

This PR adds a local method to the BorderBoxControl element and checks for the theme setting in a similar manner that other settings are being checked and set.

I've tried to make it as close as possible to the implementation in the ColorPanelDropdown element, see related code:

• getting the value: https://github.com/WordPress/gutenberg/blob/trunk/packages/block-editor/src/components/global-styles/color-panel.js#L332
• passing the value: https://github.com/WordPress/gutenberg/blob/trunk/packages/block-editor/src/components/global-styles/color-panel.js#L742

Testing Instructions

1. Make sure you're working with a custom theme.json file, and that you have the settings.color.custom property set to false (see screenshots)
2. Open the Outline for the block editor
3. Insert or select a Group Block
4. Open the right sidebar Inspector
5. Scroll to the "Border & Shadow" panel section
6. Click on the Border button trigger (see screenshots)
7. You should not see the custom color picker
8. Change the value in the theme.json to be true or remove it completely, reload the page, and repeat steps 3 to 6, at this point you should see the custom color picker.

Testing Instructions for Keyboard

1. Make sure you're working with a custom theme.json file, and that you have the settings.color.custom property set to false (see screenshots)
2. Tab to select the group block in the block editor or Outline
3. Open the Inspector with CMD + Shift + , on a Mac or Ctrl + Shift + , on a PC.
4. Tab until you get to the Border button trigger labeled Border color and style picker
5. Hit Enter or Spacebar on your keyboard
6. You should not be able to see or select the custom color picker
7. Change the value in the theme.json to be true or remove it completely, reload the page, and repeat steps 3 to 6, at this point you should see the custom color picker.

Screenshots or screencast

Before	After

Also note that it respects setting to true and if it's removed

True	Removed

[github-actions]

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[github-actions]

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Co-authored-by: annezazu <annezazu@git.wordpress.org>
Co-authored-by: cbravobernal <cbravobernal@git.wordpress.org>
Co-authored-by: vraja-pro <vrajadas@git.wordpress.org>
Co-authored-by: n8finch <n8finch@git.wordpress.org>
Co-authored-by: andreawetzel <awetz583@git.wordpress.org>

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[github-actions]

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