buffer_cache: Return handles instead of pointer to handles

externals: Use shared libraries if possible

This is mostly done by pkgconfig.
I've focused on the larger and more stable libraries.

Neither core nor web_services use OpenSSL nor LibreSSL.
However they need to link them as it's a requirement of httplib.
So let's declare this within httplib instead of core and web_services.

service: time: Implement CalculateStandardUserSystemClockDifferenceByUser.

The original idea of returning pointers is that handles can be moved.
The problem is that the implementation didn't take that in mind and made
everything harder to work with. This commit drops pointer to handles and
returns the handles themselves. While it is still true that handles can
be invalidated, this way we get an old handle instead of a dangling
pointer.

This problem can be solved in the future with sparse buffers.

decode/shift: Remove unused variable within Shift()

surface_view: Add missing operator!= to ViewParams

gl_device: Mark stage_swizzle as constexpr

surface_base: Make IsInside() a const member function

control_flow: Make use of std::move in TryInspectAddress()

Removes a redundant variable that is already satisfied by the IsFull()
utility function.

Provides logical symmetry to the interface.

This doesn't modify internal state, so this can be made const.

video_core: Amend doxygen comment references

Eliminates redundant atomic reference count increments and decrements.

Fixes broken documentation references.

Previously this was mutable even though it shouldn't be.

Texture Cache: Read current data when flushing a 3D segment.

shader/memory: Implement RED.E.ADD and minor changes to ATOM

CMakeLists: Make -Wreorder a compile-time error

This can result in silent logic bugs within code, and given the amount
of times these kind of warnings are caused, they should be flagged at
compile-time so no new code is submitted with them.

gl_rasterizer: Implement constant vertex attributes

This PR corrects flushing of 3D segments when data of other segments is
mixed, this aims to preserve the data in place.

maxwell_to_vk: Add uint16 vertex formats

gl_shader_cache: Use CompileDepth::FullDecompile on GLSL

gl_texture_cache: Fix layered texture attachment base level

shader/arithmetic: Add FCMP_CR variant

Revert "gl_shader_decompiler: Implement merges with bitfieldInsert"

vk_blit_screen: Initialize all members in VkPipelineViewportStateCreateInfo

Avoid invalid fallbacks.

When the dynamic state is specified, pViewports and pScissors are
ignored, quoting the specification:

  pViewports is a pointer to an array of VkViewport structures, defining
  the viewport transforms. If the viewport state is dynamic, this member
  is ignored.

That said, AMD's proprietary driver itself seem to read it regardless of
what the specification says.

vk_rasterizer: Default to 1 viewports with a size of 0

This is a simple optimization as Buffer Copies are mostly used for texture recycling. They are, however, useful when games abuse undefined behavior but most 3D APIs forbid it.

- Used by Animal Crossing: New Horizons.

This reverts commit 05cf2708.

Apparently the first approach using floats instead of bitfieldInert
worked better for Fire Emblem: Three Houses. Reverting to get that
behavior back.

Adds another variant of FCMP.

service: friend: Stub IFriendService::GetBlockedUserListIds.