Preserve multiline semantics on Rails/Presence

Similar issue: rubocop/rubocop#10784

Before
```diff
if a.present?
+^^^^^^^^^^^^^ Use `a.presence || b.to_f * 12.0` instead of `if a.present?
+  a
+else
+  b
+end`.
  a
else
  b
end
```

After
```diff
if a.present?
+^^^^^^^^^^^^^ Use `a.presence || b` instead of `if a.present? ... end`.
  a
else
  b.to_f + 12.0
end
```

changelog/change_preserve_multiline_semantics_on_rails_presence.md

@@ -0,0 +1 @@
+* [#x](https://github.com/rubocop/rubocop-rails/pull/x): Preserve multiline semantics on `Rails/Presence`. ([@ydah][])

lib/rubocop/cop/rails/presence.rb

@@ -106,7 +106,17 @@ def ignore_other_node?(node)
         end
 
         def message(node, receiver, other)
-          format(MSG, prefer: replacement(receiver, other), current: node.source)
+          prefer = replacement(receiver, other).gsub(/^\s*|\n/, '')
+          current = current(node).gsub(/^\s*|\n/, '')
+          format(MSG, prefer: prefer, current: current)
+        end
+
+        def current(node)
+          if node.source.include?("\n")
+            "#{node.loc.keyword.with(end_pos: node.condition.loc.selector.end_pos).source} ... end"
+          else
+            node.source
+          end
         end
 
         def replacement(receiver, other)