fix(optimizer): downgrade csso

[barak007]

So it turns out csso@5 which uses css-tree@2 is kind of broken for our case that uses the tpa-processor. it removes whitespace where it (maybe) should not.

I also opened issue in csso repo:
css/csso#447

We might not want to merge this and solve it from outside

[barak007]

So after thinking about this issue a little more I think that we should not downgrade and instead allow our integrations to accept minifier from outside at first stage and remove the built-in minifier next major

[barak007]

So it turns out we have a way to override the minify function from the outside so no work should be done here.