Memory hog: ConstraintDefinitionImpl should be static

Change-Id: I22e61fc030b0a4e004bb078c4ea29b950a9b7f7b
Signed-off-by: Robert Varga <rovarga@cisco.com>
Memory hog: ImmutableSet is appropriate here

Change-Id: Idf204d69636af931c1e2cd454528a276947f29d9
Signed-off-by: Robert Varga <rovarga@cisco.com>
Memory hog: these collections are not fields

This builder collections are only used in build() and not used
afterwards. Do not store them in the object, such that they can be freed
as soon as possible.

Change-Id: Iffad875b618f4cecbcda424c6f75275046189c90
Signed-off-by: Robert Varga <rovarga@cisco.com>