Get rid of one more jQuery dependant and have a nicer color picker as
well.
Now there is only a single global color picker init because that is all
that's necessary because the elements are present on the page when the
init code runs. The init is slightly weird because the module only takes
a selector instead of DOM elements directly.
The label modals now also perform form validation because previously it
was possible to trigger a 500 error `Color cannot be empty.` by clearing
out the color value on labels.
<img width="867" alt="Screenshot 2024-03-25 at 00 21 05"
src="https://github.com/go-gitea/gitea/assets/115237/71215c39-abb1-4881-b5c1-9954b4a89adb">
<img width="860" alt="Screenshot 2024-03-25 at 00 20 48"
src="https://github.com/go-gitea/gitea/assets/115237/a12cb68f-c38b-4433-ba05-53bbb4b1023e">
Ran most of the Less files through the Less compiler and Prettier and
then followed up with a round of manual fixes.
The Less compiler had unfortunately stripped all `//` style comments
that I had to restore (It did preserve `/* */` comments). Other fixes
include duplicate selector removal which were revealed after the
transpilation and which weren't caught by stylelint before but now are.
Fixes: https://github.com/go-gitea/gitea/issues/15565
