* There have been no changes to the code except for:
- class is now called ParsoidImageMap with a matching file name
- the namespace is changed to MediaWiki\Extension\ImageMap.
- adding phan directives to deal with Parsoid's DOM proxies
which phan doesn't seem to be see here.
* Parsoid's SiteConfig extension registration code simply overwrites
the extConfig array for a tag name. So, keeping the config and
implementation identical ensures that no matter which version of
code is registered (based on load order), we get the same behavior.
* Once this rolls out on the next train, we can remove the code
from Parsoid.
* Future patches might refactor the two implementations to extract
common functionality or merge code into a single file.
Change-Id: I6cffa4420d2daa70174fa926d5c7a4d983792969
