Add support for external grammar injections

Support Vuejs file (fix #6290)

this new setting, which defaults to false, allows to keep peek editors on  double click and ESC. This is useful for serious coding inside peek windows

Rename Css -> CSS

Fixes #6628: Add `isBuiltin` flag to language feature registration to get the previous sorting/behaviour for builtin language supports

This reverts commit 9ce57e70.

[folding] Added fold and unfold recursively to foldings

[css] Fixed slightly misleading description of all CSS margin properties

add support for css variables

Adding extra file extensions/names to ini and shell script extensions