(bug 44574, 44575) EntityData: filename-like syntax

This allows the revision ID and desired format to be used by
Special:EntityData using a filename-like syntax, e.g.:

* Special:EntityData/q1234
* Special:EntityData/q1234.json
* Special:EntityData/q1234:98765.json

Change-Id: I247191817f06e196091db0627f77af325f079651
Merge "(bug 44574, 44575) EntityData: filename-like syntax"