Add new contrast-color feature (web-platform-dx#2304)

* Add new contrast-color feature

* Remove BCD key

* Reserver contrast-color and make discouraged color-contrast

Author: captainbrosset

features/color-contrast.yml

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+name: color-contrast()
+description: "The `color-contrast()` CSS function picks a color from a list that has the most contrast with another color."
+spec: https://drafts.csswg.org/css-color-5/#contrast-color
+group: color-types
+discouraged:
+  # See these CSSWG discussions
+  # https://github.com/w3c/csswg-drafts/issues/7557
+  # https://github.com/w3c/csswg-drafts/issues/7359
+  according_to:
+    - https://github.com/w3c/csswg-drafts/issues/7557
+    - https://github.com/w3c/csswg-drafts/commit/36594e9e8496a5ca83f1f1ee2b4a83bcdf28753b
+  alternatives:
+    - contrast-color

features/color-contrast.yml.dist

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+# Generated from: color-contrast.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support: {}

features/contrast-color.yml

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+name: contrast-color()
+description: "The `contrast-color()` CSS function picks a color that has guaranteed contrast against a specified foreground or background color."
+spec: https://drafts.csswg.org/css-color-6/#funcdef-contrast-color
+group: color-types

features/contrast-color.yml.dist

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+# Generated from: contrast-color.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support: {}