Twenty Ten: Custom colors should override :visited link styles on blocks.

Make sure the block editor custom colors in the theme also override the theme's `:visited` link styles. This prevents contrast issues, like in the button block -- when the background is dark, the purple `:visited` link can be difficult to read.

Props laurelfulford.

Merges [44188] into trunk.

Fixes #45434.
Built from https://develop.svn.wordpress.org/trunk@44299


git-svn-id: https://core.svn.wordpress.org/trunk@44129 1a063a9b-81f0-0310-95a4-ce76da25c4cd