Use Capybara methods to find/click/check links

We applied the Capybara/SpecificMatcher in commit f52a86b46.  However,
this rule doesn't convert methods finding <a> tags to methods finding
links because <a> tags only count as links when they've got the `href`
attribute. For instance, in the `xss_spec.rb` file we check what happens
when clicking on an anchor tag because we're testing that the `href`
attribute has been removed and so we can't use `click_link`.

So, basically, we can't enable a rule to automatically detect when we're
using `have_css` instead of `have_link`, but we should still do it
because `have_link` adds an extra check which affects accessibility
since it makes sure the tag has the `href` attribute and so it's
recognizable as a link by screen readers.

spec/system/management/proposals_spec.rb

@@ -110,7 +110,7 @@ describe "Proposals" do
       expect(page).to have_content(proposal1.title)
       expect(page).to have_content(proposal1.summary)
       expect(page).not_to have_content(proposal2.title)
-      expect(page).to have_css("a[href='#{management_proposal_path(proposal1)}']", text: proposal1.title)
+      expect(page).to have_link proposal1.title, href: management_proposal_path(proposal1)
     end
   end
 
@@ -133,9 +133,9 @@ describe "Proposals" do
 
     within(".proposals-list") do
       expect(page).to have_css(".proposal", count: 2)
-      expect(page).to have_css("a[href='#{management_proposal_path(proposal1)}']", text: proposal1.title)
+      expect(page).to have_link proposal1.title, href: management_proposal_path(proposal1)
       expect(page).to have_content(proposal1.summary)
-      expect(page).to have_css("a[href='#{management_proposal_path(proposal2)}']", text: proposal2.title)
+      expect(page).to have_link proposal2.title, href: management_proposal_path(proposal2)
       expect(page).to have_content(proposal2.summary)
     end
   end