Add and apply Capybara/VisibilityMatcher rule

This rule was added in rubocop-rspec 1.39.0. The `visible: false` option
is equivalent to `visible: :all`, but we generally use it meaning
`visible: :hidden` for positive expectations and `visible: :all` for
negative expectations.

The only exceptations are tests where we count the number of map icons
present. I'm assuming in this case we care about the number of map icons
independently on whether they are currently shown in the map, so I'm
keeping the `visible: :all` behavior in this case.

.rubocop.yml

@@ -26,6 +26,9 @@ Capybara/FeatureMethods:
     - scenario
     - xscenario
 
+Capybara/VisibilityMatcher:
+  Enabled: true
+
 FactoryBot/AttributeDefinedStatically:
   Enabled: true