HSEARCH-1552 [50% done] Allow loading of additional "built-in bridges" via autodiscovery

Do you like where this is going?

A few notes. The discovery will happen via Service Loader but that is the easy bit.
The hard bit is to offer a `BridgeProvider` contract that does provide enough information but with a manageable API. I decided to first work on the modularisation of `BridgeFactory`.
Note that the current API will blow up when free-form entity comes into play but the while `BridgeFactory` is impacted.