Fix CPU Core Count detection and Enable Parallel Shader Compilation

This does this following things:

- Default to the runtime automatic number of threads for pre-compiling shaders
- Adds a distinct automatic thread count computation for pre-compilation  (which has less other things going on
and should scale better beyond 4 cores)
- Removes the unused logical_core_count field from the CPU detection
- Changes the semantics of num_cores from maximaum addressable number of cores to actually available CPU cores
(which is also how it was actually used)
- Updates the computation of the HTT flag now that AMD no longer lies about it for its Zen processors
- Background shader compilation is *not* enabled by default

Source/Core/Core/Config/GraphicsSettings.cpp

@@ -85,7 +85,7 @@ const Info<ShaderCompilationMode> GFX_SHADER_COMPILATION_MODE{
     {System::GFX, "Settings", "ShaderCompilationMode"}, ShaderCompilationMode::Synchronous};
 const Info<int> GFX_SHADER_COMPILER_THREADS{{System::GFX, "Settings", "ShaderCompilerThreads"}, 1};
 const Info<int> GFX_SHADER_PRECOMPILER_THREADS{
-    {System::GFX, "Settings", "ShaderPrecompilerThreads"}, 1};
+    {System::GFX, "Settings", "ShaderPrecompilerThreads"}, -1};
 const Info<bool> GFX_SAVE_TEXTURE_CACHE_TO_STATE{
     {System::GFX, "Settings", "SaveTextureCacheToState"}, true};