[Shader] Feature set, Variant collection ,Compiling, Loading

[roeas]

• Treate shader features as a set to handle mutually exclusive keywords. Shader Feature Set #378
• Use shader collections to guide the compiling and loading of shader variants. Shader Variant Collections Frame #381 Shader lazy load #382
• Modify shader files to hot-compile and hot-load variants when editor is running.
  • Block the main process from compiling uber shaders only when the editor regains focus. SDL window focus. #377 Shader hot compile and reload #421
  • Store shader dependencies and update them appropriately.
    convert to [Resource Level] Resources Manager and meta file #442

[roeas]

Discussion on feature set and variant collection: #362
Hot load: #241
Unity Loading, Prewarming and Chunk: https://docs.unity3d.com/2023.2/Documentation/Manual/shader-loading.html