[gltf] Add glTF2 loader and pbr renderer

[IAmNotHanni]

Closes #256
Closes #268
Closes #429

Let there be glTF2 models

Work in progress!

I am adapting the glTF2 loader from Sascha Willem's sample repository. This work will not include model animations, physically based rendering or other components of glTF2 we're not supporting yet.

TODO

• Write a glTF2 loader class using tinygltf
• Modify descriptor pattern so it allows for multiple images to be passed in
• Fix all clang-tidy warnings!
• Add automatic tests (inexor-vulkan-renderer-tests)
• Add benchmarks (inexor-vulkan-renderer-benchmarks)
• Squash before opening pull request

Sorting this massive PR

I will have to make smaller pull requests out of this one, otherwise it's too big.
Here is a list of things I changed:

• Added ktx dependency
• Added ShaderLoader wrapper and don't load shaders through TOML file
• Added glTF2 data structure files...
• Added Cubemaps
• Added glTF2 loader
• Refactored rendering: separate data loading from rendering.
• Refactored rendering: Render octree in new rendergraph style
• Refactor rendergraph setup function
• Added new methods to rendergraph and other small refactorings (builder pattern)
• Added wrapper for loading glTF2 files (based on tinygltf)
• Added wrapper for glTF2 model data parsing
• Added glTF2 pbr renderer
• Added new shaders for skybox
• Added new shaders for pbr, including BRDFLUT and cubemaps
• Refactored ImGui to use ShaderLoader
• Added BRDF lookup table generator
• Fixed a bug in descriptor builder pattern (binding index!)
• Added DescriptorPool wrapper
• Refactored GpuTexture a little
• Added OffscreenFramebuffer (required for cubemaps)
• Fixed a bug in rendergraph
• Added new representations (object type to string_view)
• ...

[IAmNotHanni]

• Rebase onto master

[IAmNotHanni]

• Add nolints for pointer arithmetics

[IAmNotHanni]

yeetari: just taking a look at the gltf PR - we preferably want to avoid the std::vectors and such completely when loading the textures

[IAmNotHanni]

• Rebase onto master

[IAmNotHanni]

• Rebase onto master

[IAmNotHanni]

• Rebase onto master