feat(lint): add prettier formatter to assert LESS files whitespaces

[mvorisek]

Compared to Stylelint, Prettier is very simple tool and I am quite supprised Stylelint is deprecating the whitespace rules in favor of Prettier. For LESS it seems ok, for JS, we should never enable Prettier as formatting is part of a code and improves readability.

As Prettier is an opinionated formatter instead of an linter, we need to satisfy it everywhere without exceptions.

When I was crafting this PR, I found several Prettier issues and proposed changes to Prettier:

• Fix semicolon duplicated at the end of LESS file prettier/prettier#14007
• Fix no space after unary minus when followed by opening parenthesis in LESS prettier/prettier#14008
• Do not change case of property name if inside a variable declaration in LESS prettier/prettier#14034

In this PR, these changes are contained and Prettier is patched before it is run. Once the changes are merged in prettier and stable release is made, they can be removed.

This PR fixes minor whitespaces unfixed/undetected in GH-2610.

And also asserts:

• PHP port of the LESS fails to compile colors.less #1832
• feat(lint): add stylelint overrides and variation files #2593 (comment)

Prettier has no built in support to dump the diff - prettier/prettier#6885 - so we dump it in the CI using git.

[mvorisek]

PR is done, Prettier fixes with patches looks reasonable. Compiled semantic.min.css is binary the same as before this PR.

[lubber-de]

Please resolve conflicts

[lubber-de]

In this PR, these changes are contained and Prettier is patched before it is run. Once the changes are merged in prettier and stable release is made, they can be removed.

Seriously? This is really hacky. You want to use a tool, which does not do what we need... Why not fork prettier.io instead and use that?