Users should be able to add a custom gradient when the default gradients are disabled

[oandregal]

Description

The gradients panel doesn't allow user to add a custom gradient when the default gradients are disabled. The panel is empty but not hidden.

Step-by-step reproduction instructions

How to test

• Use a theme that does not provide any solids or gradients.
• Set defaultPalette and defaultGradients to false.

This is what I see for solids:

This is what I see for gradients (note that it's empty):

If I then disable the custom colors (settings.color.custom to false), this is what I see (the color panel is shown but it does not contain anything):

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[andrewserong]

I thought I'd start working on a fix for this one. I have a PR open in #36900, but I also noticed a couple of other issues with the gradient that I've raised in #36899. I'm just at the end of my week now, so I'll do some more investigating next week (I don't think it's related to my PR, but I'll do more testing next week to be sure).

[andrewserong]

The main blocker in #36899 has been resolved, so the PR to fix the main issue here (ensure a custom gradient can be added when default and theme gradients are disabled) is ready for review now: #36900