Cleans up unused includes and trims off some dependencies on externals.

* get rid of boost::optional

* Remove optional references

* Use std::reference_wrapper for optional references

* Fix clang format

* Fix clang format part 2

* Adressed feedback

* Fix clang format and MacOS build

 hle_ipc: Make GetDomainMessageHeader return a regular pointer

Gets rid of the need to call the getter and then check for null.

Nothing requires the shared owner ship here, so we can just return a
plain pointer.

core: Add missing const variants of getters for the System class

Implemented Mipmaps

time_stretch: Switch to values of Citra

video_core: Move OpenGL specific utils to its renderer

renderer_opengl: Enable alpha channel for DXT1 texture format

renderer_opengl: Correct bpp value for ASTC_2D_8X5_SRGB

Many of the Current<Thing> getters (as well as a few others) were
missing const qualified variants, which makes it a pain to retrieve
certain things from const qualified references to System.

renderer_opengl: Correct bpp value for ASTC_2D_8X5

Improved Shader accuracy on Vertex and Geometry Shaders.

Revert "Update MACOSX_DEPLOYMENT_TARGET to 10.14"

svc: Implement svcGetInfo command 0xF0000002

Update MACOSX_DEPLOYMENT_TARGET to 10.14

* remove unnecessary if-statements

* Addressed feedback

service/filesystem: Implemented DeleteDirectory & DeleteDirectoryRecursive

loader/nsp: Move secondary loader initialization to constructor

Implement sRGB support

key_manager: Use isxdigit instead of isdigit when reading key file

Crypto revisions are hex numbers and this function only checks if the string is valid for stoul in base 16, so it should be isxdigit.

configure_system: Indicate when filesystem operations fail