Remove 'cursor: not-allowed' style from buttons mixins in colors/_mixins.scss

[afercia]

In the src/wp-admin/css/colors/_mixins.scss the mixins for the ​button, ​button-secondary, and ​button-tertiary contain styling for the cursor CSS property:

cursor: not-allowed;

• Why a CSS property that is related to interaction or, better, the lack of interaction is within a file that is supposed to be about colors?
• The not-allowed cursor styling for disabled buttons is not an established pattern in WordPress. There are only 3 other occurrences in the codebase and they are minor, edge cases.
• This styling doesn't add much value and isn't native behavior. All enabled buttons already get a pointer cursor while the disabled ones get the default cursor.
• It introduces inconsistency with all the other buttons in the admin that don't use the mixins. As such, some disabled buttons show the not-allowed cursor style, while others don't.

I'd like to propose to just remove this styling.

[afercia]

Example of a button with the new not-allowed cursor style

Removes cursor: not-allowed from the primary, secondary, and tertiary button mixins. This lets disabled buttons use the existing default cursor styles for consistency across the admin.

Trac ticket: https://core.trac.wordpress.org/ticket/66251

I pushed a commit to remove the remaining 3 occurrences of cursor: not-allowed;. They are all very edge cases and introduce unnecessary inconsistency anyways.

1
In the Custom widgets page, only the 'Custom HTML` widget used it when the button so save is disabled:

2
In the Theme / Plugin file editors. It was used on 'Update File' button when disabled:

3
In the Customizeer, when reordering menus or widgets, it was used for the 'Add Items' / 'Add Widgets' button. This didn;t work anyways becayse pointer-events: none; already resets the cursor style:

[afercia]

Thank you @sainathpoojary for the PR.

I added a commit to remove the remaining occurrences. They are all unnecessary edge cases and only introduce more inconsistency. Documented in the PR comment above.

[afercia]

In 64229:

Administration: Improve consistency of the disabled buttons styling.

A few buttons had the cursor: not-allowed; style applied, which has now been removed. This styling is unnecessary and only introduces inconsistency with other disabled buttons styling.

For the removed styles in colors/_mixins.scss it is also worth noting that a style related to interaction should not live in a file that contains mixins dedicated to colors.

• Removes the cursor: not-allowed style from buttons mixins in colors/_mixins.scss.
• Removes the remaining 3 occurrences for the classic 'Custom HTML' widget, the Theme / Plugin file editors and in the Customizer when reordering menus or widgets.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/14040

Props sainathpoojary, dhruvang21, afercia.
Fixes #66251.