GAPI: Add OAK backend

* Initial tests and cmake integration

* Add a public header and change tests

* Stub initial empty template for the OAK backend

* WIP

* WIP

* WIP

* WIP

* Runtime dai hang debug

* Refactoring

* Fix hang and debug frame data

* Fix frame size

* Fix data size issue

* Move test code to sample

* tmp refactoring

* WIP: Code refactoring except for the backend

* WIP: Add non-camera sample

* Fix samples

* Backend refactoring wip

* Backend rework wip

* Backend rework wip

* Remove mat encoder

* Fix namespace

* Minor backend fixes

* Fix hetero sample and refactor backend

* Change linking logic in the backend

* Fix oak sample

* Fix working with ins/outs in OAK island

* Trying to fix nv12 problem

* Make both samples work

* Small refactoring

* Remove meta args

* WIP refactoring kernel API

* Change in/out args API for kernels

* Fix build

* Fix cmake warning

* Partially address review comments

* Partially address review comments

* Address remaining comments

* Add memory ownership

* Change pointer-to-pointer to reference-to-pointer

* Remove unnecessary reference wrappers

* Apply review comments

* Check that graph contains only one OAK island

* Minor refactoring

* Address review comments