Selectors- CSS Selectors initial support (#2170)

Co-authored-by: Florian Scholz <[email protected]>

Author: jamesnw

features/selectors.yml

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+name: Selectors (core)
+description: CSS selectors match elements based on their type, attributes, and relationship to other elements. They define the specific elements to which a block of styles will be applied. This feature represents the oldest selectors of CSS.
+spec: https://drafts.csswg.org/selectors-4/
+group: selectors
+compat_features:
+  - css.selectors.child
+  - css.selectors.class
+  - css.selectors.descendant
+  - css.selectors.id
+  - css.selectors.list
+  - css.selectors.next-sibling
+  - css.selectors.type
+  - css.selectors.universal
+  - css.selectors.type.namespaces
+  - css.selectors.universal.namespaces
+  - css.selectors.attribute
+  - css.selectors.subsequent-sibling

features/selectors.yml.dist

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+# Generated from: selectors.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: high
+  baseline_low_date: 2015-07-29
+  baseline_high_date: 2018-01-29
+  support:
+    chrome: "1"
+    chrome_android: "18"
+    edge: "12"
+    firefox: "1"
+    firefox_android: "4"
+    safari: "3"
+    safari_ios: "1"
+compat_features:
+  # baseline: high
+  # baseline_low_date: 2015-07-29
+  # baseline_high_date: 2018-01-29
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "1"
+  #   safari_ios: "1"
+  - css.selectors.child
+  - css.selectors.class
+  - css.selectors.descendant
+  - css.selectors.id
+  - css.selectors.list
+  - css.selectors.next-sibling
+  - css.selectors.type
+  - css.selectors.universal
+
+  # baseline: high
+  # baseline_low_date: 2015-07-29
+  # baseline_high_date: 2018-01-29
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "1.3"
+  #   safari_ios: "1"
+  - css.selectors.type.namespaces
+  - css.selectors.universal.namespaces
+
+  # ⬇️ Same status as overall feature ⬇️
+  # baseline: high
+  # baseline_low_date: 2015-07-29
+  # baseline_high_date: 2018-01-29
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "3"
+  #   safari_ios: "1"
+  - css.selectors.attribute
+  - css.selectors.subsequent-sibling