Add aria-label to markers in admin map settings

We forgot to do so in commit b896fc4bb. Back then, we said:

> Note that we aren't providing a proper aria-label for markers on the
> map we use in the form to create a proposal or an investment. Adding
> one isn't trivial given the current code, and keyboard users can't add
> a marker in the first place. We'll have to revisit this issue when we
> add keyboard support for this.

However, in the admin section, the marker is already there, so it should
have a label. In this case, we're using the coordinates as label because
it's the most relevant text for the marker in the context of a form. We
could also use "Default map location" instead, but that information is
already present on the page.

Axe was reporting the same accessibility error we mentioned in commit
b896fc4bb in this situation.

spec/components/shared/map_location_component_spec.rb

@@ -28,4 +28,48 @@ describe Shared::MapLocationComponent do
       expect(page).to have_button "Remove map marker"
     end
   end
+
+  describe "marker title" do
+    it "uses the mappable title when there's a mappable with a title" do
+      map_location = build(
+        :map_location,
+        proposal: Proposal.new(title: "Meet me here"),
+        latitude: "25.25",
+        longitude: "13.14"
+      )
+
+      render_inline Shared::MapLocationComponent.new(map_location)
+
+      expect(page).to have_css "[data-marker-title='Meet me here']"
+    end
+
+    it "uses the coordinates when there's no mappable" do
+      map_location = build(:map_location, latitude: "25.25", longitude: "13.14")
+
+      render_inline Shared::MapLocationComponent.new(map_location)
+
+      expect(page).to have_css "[data-marker-title='Latitude: 25.25. Longitude: 13.14']"
+    end
+
+    it "uses the coordinates when the mappable has an empty title" do
+      map_location = build(
+        :map_location,
+        proposal: Proposal.new(title: ""),
+        latitude: "25.25",
+        longitude: "13.14"
+      )
+
+      render_inline Shared::MapLocationComponent.new(map_location)
+
+      expect(page).to have_css "[data-marker-title='Latitude: 25.25. Longitude: 13.14']"
+    end
+
+    it "is not present when the map location isn't available" do
+      map_location = build(:map_location, latitude: "25.25", longitude: nil)
+
+      render_inline Shared::MapLocationComponent.new(map_location)
+
+      expect(page).not_to have_css "[data-marker-title]"
+    end
+  end
 end

spec/system/admin/settings_spec.rb

@@ -60,6 +60,7 @@ describe "Admin settings", :admin do
 
       expect(page).to have_field "Latitude", with: "51.48"
       expect(page).to have_field "Longitude", with: "0.0"
+      expect(page).to have_css ".map-icon[aria-label='Latitude: 51.48. Longitude: 0.0']"
 
       within "#map-form" do
         find(".map-location").click
@@ -68,7 +69,9 @@ describe "Admin settings", :admin do
 
       expect(page).to have_content "Map configuration updated successfully"
       expect(page).to have_field "Latitude"
+      expect(page).to have_css ".map-icon"
       expect(page).not_to have_field "Latitude", with: "51.48"
+      expect(page).not_to have_css ".map-icon[aria-label='Latitude: 51.48. Longitude: 0.0']"
     end
   end