BUG-1485: make AbstractRangeGenerator deal with GTOs

BUG-1485: make AbstractRangeGenerator deal with GTOs

For enforcement of ranges in builders, we will need to deal with types
other than ConcreteType. Also clean up internal interfaces, add some
javadocs and remove some trailing whitespace.

Also perform Number class conversion silently if it does not result in
loss of precision. Emit a warning if it does.

Change-Id: I8f3ba96c104fb28f6d2cfc4b05b5d24bb7f80aa1
Signed-off-by: Robert Varga <rovarga@cisco.com>
(cherry picked from commit d8f544b093f024ff156873c66eebf976f6738382)