Increase cmake_minimum_required to 3.19

[mmassing]

Generator expressions for multiple configurations are only supported since cmake 3.19.
When using older cmake versions, this leads to errors such as:

CMake Error at Graphics/GraphicsTools/CMakeLists.txt:90 (target_link_libraries):
Error evaluating generator expression:

$<CONFIG:Release,RelWithDebInfo>

To give more actionable error messages, the cmake_minimum_required should be increased.

Probably affects other parts of DiligentEngine as well.

[TheMostDiligent]

Fixed in 36f4628