HSEARCH-1552 Make BridgeProvider not depend on annotated element

Make private bridge providers extend a specific subclass not exposed to users.
HSEARCH-1552 Move NumericFieldBridge into a dedicated provider
HSEARCH-1552 Loop through defined provider and raises exception for duplicates
HSEARCH-1552 Add ServiceLoader lookup for custom BridgeProviders
HSEARCH-1552 Check validity of return type when the Tika bridge is built rather than at execution
HSEARCH-1552 Remove ContainerType.UNKNOWN (case identified)
Minor wording adjustment (define -> declare)
HSEARCH-1552 Add documentation for BridgeProvider
HSEARCH-1552 Experiment on splitting the BridgeProvider contract in canDo() and do()

I did not spend too much time on it.
I did not remove the do() safeguards as I felt a defensive code would be
the natural tendency of a user.