Update `postcss-less` to v2 (#6778)
* Update `postcss-less` to v2
* fix less `custom-selectors`
* fix less `custom-selectors` 2
* fix custom-selector `:` position
* remove less hack
* fix custom selector
* cleanup
* add changlog
* add link
* restore changlog
* restore snap
* restore snap
* update postcss-custom-selectors detect
* remove startsWith
* trigger build
* update `custom-selector`
* add test and changelog
* style
* md
* issue-4090-test
* docs
* Update CHANGELOG.unreleased.md
Co-Authored-By: Georgii Dolzhykov <thorn.mailbox@gmail.com>
* fix pr issue
* fix
* fix merge issue
* insert new line
* snap update
* only support custom-selector in css
* scss already parse it as custom-selector
* remove `custom-selector` test in scss
* link
