feat(spec): reject an unknown object-selector key in the web runtime

Same rule and the same message as the native side: a key no element can
carry throws instead of matching nothing. The accepted list is one list,
committed as a fixture both suites assert, so a spec cannot be accepted
by one runtime and rejected by the other.

pkg/spec/test/fixtures/selector-keys.json

@@ -0,0 +1,38 @@
+[
+  "accessibilityIdentifier",
+  "accessibilityLabel",
+  "accessibilityText",
+  "aria-label",
+  "ariaLabel",
+  "bounds",
+  "checked",
+  "class",
+  "className",
+  "clickable",
+  "content-desc",
+  "contentDescription",
+  "data-testid",
+  "desc",
+  "descPrefix",
+  "editable",
+  "elementType",
+  "enabled",
+  "focused",
+  "hintText",
+  "id",
+  "idPrefix",
+  "identifier",
+  "label",
+  "package",
+  "placeholder",
+  "placeholderValue",
+  "resource-id",
+  "scrollable",
+  "selected",
+  "tag",
+  "testID",
+  "testTag",
+  "text",
+  "title",
+  "value"
+]