constellation: focusing and closing webviews (#30842)

* constellation: focusing, closing, and native window visibility

* rename “browser” to “webview”, “unfocus” to “blur”

* remove native window visibility from constellation

* rename more “browser” to “webview”

* guard clauses

* don’t automatically focus when no webviews are focused

* comment spec steps for window.close()

* use format interpolation

Co-authored-by: Martin Robinson <mrobinson@igalia.com>

* fix formatting

* rename “Webview” to “WebView” in types and type parameters

* remove unused method

* fix libsimpleservo

---------

Co-authored-by: Martin Robinson <mrobinson@igalia.com>

python/servo/testing_commands.py

@@ -138,6 +138,7 @@ class MachCommands(CommandBase):
             "servo_config",
             "servo_remutex",
             "crown",
+            "constellation",
         ]
         if not packages:
             packages = set(os.listdir(path.join(self.context.topdir, "tests", "unit"))) - set(['.DS_Store'])