Twenty Twenty-One: Replace the experimental link color theme support

[poena]

In functions.php, replace add_theme_support( 'experimental-link-color' );
with add_theme_support( 'link-color' );

I am listing this as bug because add_theme_support( 'experimental-link-color' ); will throw a "doing it wrong" message when Gutenberg version 16.2 (currently in development) is active.
The message is intentionally in the Gutenberg plugin, not core, because 'experimental-link-color' was introduced in Gutenberg, and core support was limited.

Follow up to https://core.trac.wordpress.org/ticket/58597.

[poena]

Replaces the experimental theme support and adds the new link color theme support

[poena]

Removes the experimental theme support without replacement

[poena]

I have uploaded two patches. The second option removes the theme support to prevent the doing it wrong message, but does not add the new theme support. This second option would give contributors more time to test and fix any CSS issues related to the link color theme support.

Testing instructions

To reproduce the warning, you need Gutenberg version 16.2 or newer, downloadable from ​https://github.com/WordPress/gutenberg/

Activate the plugin and the theme and visit the WordPress admin area.

[mukesh27]

This ticket was discussed during the bug scrub.

Manual testing is required for this task. Please ping @ironprogrammer and @webtechpooja to coordinate and perform the necessary tests.

[audrasjb]

After applying 58702.diff

[audrasjb]

58702.diff is the best option as it also introduces the feature for TT1.
Let's implement this patch :)

[audrasjb]

In 56170:

Twenty Twenty-One: Replace the experimental link color theme support.

This replaces add_theme_support( 'experimental-link-color' ) with add_theme_support( 'link-color' ), to provide the feature to Twenty Twenty-One users, but
also to avoid throwing a "doing it wrong" message when Gutenberg version 16.2 is active.

Follow-up to [58597].

Props poena.
Fixes #58702.