Add Parser Support for Auto-Detecting Links in Slice Doc-Comments

[InsertCreativityHere]

Doxygen will automatically detect and link to elements in doc-comments, even if they weren't explicitly linked to.
For example, Doxygen generates 2 links to Locator from this: /// Locator is pretty cool. {@link Locator} exists.

We should consider porting this logic over to the Slice compiler.
ie. Augment DocComment::parseFrom to automatically detect links, and call the linkFormatter on them, even if no @link was used.

[InsertCreativityHere]

We are no longer supporting auto-linking in Slice. See: #4329