This fixes the `PrettyText.make_all_links_absolute` to better handle subfolder.
In subfolder, when given the cooked version of a post, links to mentions includes the `Discourse.base_path` prefix. Adding the `Discourse.base_url` was doubling the `Discourse.base_path`.
The issue was hidden behind the specs which was stubbing `Discourse.base_url` instead of relying on `Discourse.base_path`.
This fixes both the "algorithm" used in `PrettyText.make_all_links_absolute` to better handle this case and correct the specs to properly handle subfolder cases.
There are lots of changes in the specs due to a refactoring to use squiggly heredoc strings for easier reading and less escaping.
8f7a3e5b29