- minor cosmetic changes : comments, typos

- fix perf test iterations

Support Convolution3D layer on IE backend (#14301)

* Add Convolution3D layer

* Disable CXX11

* Fixed tests

* Add Pooling3D layer

* Merge Conv2d with Conv3d and Pool2d with Pool3d layers

* Split pads

* Add Deconvolution layer

* Refactoring

* Deduplication

* Refactoring

* Add utils for Convolution and Pooling layers

* Async API for GAPI

 - naive implementation as a starting point

* Fix namespace comment in header

properly handle "check" mode with:
"--perf_min_samples=1 --perf_force_samples=1"

* Fix for Homogenous precision #14242:
 - moved scale computation to an inline function
 - use std::numeric_limits<float>::epsilon() instead of != 0.0

* Fix for Homogenous precision #14242:
 - fixed warnings for type conversion

* Fix for Homogenous precision #14242:
 - use float epsilon() for truncation of doubles

backporting commit c9f3f4d1

Avoid non-intentional call of "include(FindPkgConfig)"
It should be handled in the root CMakeLists.txt (safely for cross-compiling)