Deprecate DirectX 9 API

[Xottab-DUTY]

DirectX 9 code should be deprecated and removed from the engine.

Currently, we have two renderers on it: static lighting R1, which should be ported both to DirectX 11 (#488) and OpenGL, and dynamic lighting R2, which can be removed and replaced by R4 (it is a superset of R2 anyway)

Thing to think on: how to still support DX9 hardware? DirectX 11 with Feature Level 9?
Lower the minimal OpenGL required version?

If we will support feature level 9, then we need to implement #281.

[Xottab-DUTY]

Hmm. and we should decide how we will support #392, since Shadow of Chernobyl is completely DirectX 9 game.

Are there any shader cross-compilers from DX9 shaders to DX11 shaders?
We can use D3DCOMPILE_ENABLE_BACKWARDS_COMPATIBILITY and compile DX9-style shaders with shader model 5.0 for DX11. But it's a mandatory to implement #281.

[Xottab-DUTY]

So, if we want to support Shadow of Chernobyl with it's DX9-style shaders and/or DX9-level hardware, firsly we should fully implement #281.

[Xottab-DUTY]

DX9 should remain until new year 2020. After then we should decide if we will remove it or this issue will be cancelled and DX9 renderer will be still supported.

[Xottab-DUTY]

DX9 support will remain and still be supported.

[Xottab-DUTY]

This is likely to be reconsidered during August - September 2024.

[Xottab-DUTY]

We planned to decide whether or not to remove DX9 in September 2024, but I decided to ask the community.
Almost everyone suggested to removed it already.

So, I have removed DX9 renderer (R1 and R2) from the mainstream development branch (dev).
I also created a separate dx9 branch where I have preserved R1 renderer so that we can still experiment and make some progress with #1313 and #1314.