GS_RGBA, GS_BGRX, and GS_BGRA now use TYPELESS DXGI formats, so we can
alias them between UNORM and UNORM_SRGB as necessary. GS_RGBA_UNORM,
GS_BGRX_UNORM, and GS_BGRA_UNORM have been added to support straight
UNORM types, which Windows requires for sharing textures from D3D9 and
OpenGL. The D3D path aliases via views, and GL aliases via
GL_EXT_texture_sRGB_decode/GL_FRAMEBUFFER_SRGB.
A significant amount of code has changed in the D3D/GL backends, but the
concepts are simple. On the D3D side, we need separate SRVs and RTVs to
support nonlinear/linear reads and writes. On the GL side, we need to
set the proper GL parameters to emulate the same.
Add gs_enable_framebuffer_srgb/gs_framebuffer_srgb_enabled to set/get
the framebuffer as SRGB or not.
Add gs_linear_srgb_active/gs_set_linear_srgb to instruct sources that
they should render as SRGB. Legacy sources can ignore this setting
without regression.
Update obs_source_draw to use linear SRGB as needed.
Update render_filter_tex to use linear SRGB as needed.
Add gs_effect_set_texture_srgb next to gs_effect_set_texture to set
texture with SRGB view instead.
Add SRGB helpers for vec4 struct.
Create GDI-compatible textures without SRGB support. Doesn't seem to
work with SRGB formats.
