Simplify Feature loading code

[alandtse]

There's certain inefficiencies in the feature loading that requires a lot of duplicated code.

• Manual registration for the feature vectors. https://github.com/doodlum/skyrim-community-shaders/blob/dev/src/Feature.cpp#L70-L88
• Manual call for corresponding sections in the SKSE load process https://github.com/doodlum/skyrim-community-shaders/blob/dev/src/XSEPlugin.cpp#L99-L102.
• DrawDeferred/Draw https://github.com/doodlum/skyrim-community-shaders/blob/subsurface-scattering/src/State.cpp#L42-L45 and compare with https://github.com/doodlum/skyrim-community-shaders/blob/subsurface-scattering/src/State.cpp#L30-L34
• Clearing Shader Cache

  skyrim-community-shaders/src/Menu.cpp

  Lines 307 to 311 in edb6328

  	if (ImGui::Button("Clear Shader Cache", { -1, 0 })) {
  	shaderCache.Clear();
  	ScreenSpaceShadows::GetSingleton()->ClearComputeShader();
  	SubsurfaceScattering::GetSingleton()->ClearComputeShader();
  	}

At least for the loading section, we could require all features implement a function to call (could be blank). So DataLoaded, PostPostLoad, etc.

[FlayaN]

Can check 2-4 now with my PR, if dev branch is enough. Also added wiki documentation for the virtual functions in Feature.h https://github.com/doodlum/skyrim-community-shaders/wiki/Developers#virtual-functions

[Pentalimbed]

• Manual registration for the feature vectors

I don't think there is a better way to approach this. You have to reference the class itself at some place, and it cannot really be simpler than the current two (or three) lines: one include, one or two singleton calls.

[FlayaN]

Yeah that's why I only did 2-4. Didn't think of an nice way to finish

Manual registration for the feature vectors

Is there more details on how that can be improved? Otherwise I guess this task can be closed

[alandtse]

I'm ok with closing if we think we've done enough. Or this can just go stale in the hope someone surprises us.