New css @function feature (#2791)

* New css @function feature

* Run prettier

* Update features/function.yml

Co-authored-by: James Stuckey Weber <[email protected]>

---------

Co-authored-by: James Stuckey Weber <[email protected]>

Author: captainbrosset

features/function.yml

@@ -0,0 +1,5 @@
+name: "@function"
+description: "The `@function` CSS at-rule defines a custom function that takes CSS values or custom properties as arguments, and returns a CSS value. It can be based on conditional logic such as by using the `@media` at-rule."
+spec: https://drafts.csswg.org/css-mixins-1/#function-rule
+group: css
+# No compat keys yet, this feature is planned to ship with Chromium 139

features/function.yml.dist

@@ -0,0 +1,6 @@
+# Generated from: function.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support: {}