Reconsider if bg-opacity-* should be deprecated

[drschwabe]

You deprecated bg-opacity-* and suggest instead 'use opacity modifiers like bg-black/50'

however, this is not useful and extra work if you don't know/need to know the background color in advance.

ie- if you are programatically trying to change bg-opacity independent of color

[AnYiEE]

I also want to know how to set the background opacity without knowing the color in advance, or conversely, modify the background color without knowing the opacity; it's very convenient in v3 (e.g.), but in v4 it looks like I'll have to change many lines.

[skiabox]

I liked the new way of applying opacity.

[AnYiEE]

It is not about providing a new way (that method was already available), but rather completely removing another existing method.