This change adjusts the existing "Dark Mode Notices" and changes it into
a checkbox. This toggles a flag used to determine if the (now
separated) dark mode variables CSS should be loaded.
First Seedlet was changed so that all custom CSS variables for color
definitions are associated with the 'seedlet-custom-color-overrides'
stylesheed. (Previously only editor override styles were associated
with that stylesheet.
Next Spearhead was changed to first dequeue that stylesheet, THEN assign
the spearhead-specific style variables THEN re-enqueue that
seedlet-custom-color-overrides stylesheet.
This puts the customizer color variable assignments AFTER the Spearhead
variable assignments so that those are the values that are used.
This fixes the issue where some styles (such as the image caption) have
"dark mode" support added to them. This is fine if a user has "dark
mode" enabled for their system. But in the default mode it isn't a
"dark" style and therefore those stylistic behaviors introduce problems.
I did not notice any negative behavior due to this being removed.
This behavior seems to have been introduced due to recent chagnes in
Gutenberg that introduce additional editor styles for themes that
express support for 'dark-editor-style'.
