Revert including outline-color in transition and transition-colors by default

[reinink]

Resolves #10591

This PR reverts a change made in #10385 where we added outline-color to the transition and transition-colors utilities by default. Unfortunately this created a breaking change for people using focus:outline-none because our implementation of outline-none actually sets the outline-color to transparent instead of the outline-style to none for accessibility reasons related to Windows High Contrast Mode. This caused a black outline to momentarily appear on focus if you were using a transition or transition-colors utility on an element that also had focus:outline-none.

For anyone who does need outline-color to transition, you can extend your transitionProperty configuration to include outline-color in the DEFAULT and colors properties:

let defaultTheme = require('tailwindcss/defaultTheme')

/** @type {import('tailwindcss').Config} */
module.exports = {
  content: [...],
  theme: {
    extend: {
      transitionProperty: {
        DEFAULT: `${defaultTheme.transitionProperty.DEFAULT}, outline-color`,
        colors: `${defaultTheme.transitionProperty.colors}, outline-color`,
      }
    },
  },
  plugins: [],
}

There is a good chance we add this back for Tailwind CSS v4.0 along with this change to outline-none that only sets the outline-color to transparent when forced-colors is active:

https://play.tailwindcss.com/fFQOGafBjR

.focus\:outline-none:focus {
  outline-style: none;
}

@media screen and (forced-colors: active) {
  .focus\:outline-none:focus {
    outline: 2px solid transparent;
    outline-offset: 2px;
  }
}

We've opted not to make this change to outline-none right away so that we have more time to test it, while still correcting this breaking change right away.

[kripod]

Is there a chance a future feature flag could be added for this? Perhaps it may be called transitionOutlineColor.