Bug 1644102 - Turn on constructable stylesheets by default. r=edgar,preferences-reviewers,mstriemer

All known issues have patches. Let's try this after these land.

Differential Revision: https://phabricator.services.mozilla.com/D144570

modules/libpref/init/StaticPrefList.yaml

@@ -7330,7 +7330,7 @@
 # Whether Constructable Stylesheets are enabled in script.
 - name: layout.css.constructable-stylesheets.enabled
   type: bool
-  value: false
+  value: true
   mirror: always
 
 # Whether trigonometric constants and functions are enabled in calc().

testing/web-platform/meta/webidl/ecmascript-binding/observable-array-ownkeys.window.js.ini

@@ -1,3 +1,2 @@
 [observable-array-ownkeys.window.html]
-  [ObservableArray's ownKeys trap]
-    expected: FAIL
+  prefs: [layout.css.constructable-stylesheets.enabled:true]

toolkit/components/featuregates/Features.toml

@@ -40,7 +40,7 @@ preference = "layout.css.constructable-stylesheets.enabled"
 type = "boolean"
 bug-numbers = [1520690]
 is-public = {default = false, nightly = true}
-default-value = false
+default-value = true
 
 [devtools-compatibility-panel]
 title = "experimental-features-devtools-compatibility-panel"