gpu_thread: Don't spin wait if there are no GPU commands.

* kernel: Replace usage of boost::intrusive_ptr with std::shared_ptr for kernel objects.

- See https://github.com/citra-emu/citra/pull/4710 for details.

gl_shader_cache: Miscellaneous changes to shaders

maxwell_3d: Fix stencil_back_func_mask offset

svc: GetSystemTick should return cntpct_el0, not core ticks.

Port citra-emu/citra#4964: "Unfold UNREACHABLE implementation for dumb compilers"

buffer_cache: Remove brace initialized for objects with default constructor

Kernel: Correct behavior of Condition Variables to be more similar to real hardware.

gl_shader_gen: Apply default value to gl_Position

Kernel: Correct Cancel Synchronization.

We relies on UNREACHABLE's noreturn attribute to eliminate parent's "no return value" warning. However, this was wrapped in a `if(!false)` block, which compilers may not unfold to recognize the noreturn nature.

SSBOs and other resources are limited per pipeline on Intel and AMD.
Heuristically reserve resources per stage having in mind the reported
OpenGL limits.

glBindTextureUnit doesn't support null textures. Skip binding these.

Intel's proprietary driver enters in a corrupt state when compute
shaders are executed. For now, disable these.

The current shared memory size seems to be smaller than what the game
actually uses. This makes Nvidia's driver consistently blow up; in the
case of FE3H it made it explode on Qt's SwapBuffers while SDL2 worked
just fine. For now keep this hack since it's still progress over the
previous hardcoded shared memory size.

Stage and compute shaders were using a different binding counter.
Normalize these.

Images were not being bound to draw invocations because these would
require a cache invalidation.

Local memory size in compute shaders was stubbed with an arbitary size.
This commit specializes local memory size from guest GPU parameters.

Shared memory was being declared with an undefined size. Specialize from
guest GPU parameters the compute shader's shared memory size.

Drop the usage of ARB_compute_variable_group_size and specialize compute
shaders instead. This permits compute to run on AMD and Intel
proprietary drivers.

Some games like "Fire Emblem: Three Houses" bind 2D textures to offsets
used by instructions of 1D textures. To handle the discrepancy this
commit uses the the texture type from the binding and modifies the
emitted code IR to build a valid backend expression.

E.g.: Bound texture is 2D and instruction is 1D, the emitted IR samples
a 2D texture in the coordinate ivec2(X, 0).

Instead of specializing shaders to separate texture buffers from 1D
textures, use the locker to deduce them while they are being decoded.

Port citra-emu/citra#4953: "citra_qt/main.ui: remove unused actions "Load Symbol Map..." and "Select Game Directory...""

service/am: Remove unnecessary Skip calls

am: Stub QueryApplicationPlayStatistics

When the target is 0, all threads must be processed.

This commit ensures cond var threads act exactly as they do in the real
console. The original implementation uses an RBTree and the behavior of
cond var threads is that at the same priority level they act like a
FIFO.

shader/other: Reduce DEPBAR log severity

While DEPBAR is stubbed it doesn't change anything from our end. Shading
languages handle what this instruction does implicitly. We are not
getting anything out fo this log except noise.

Nvidia has sane default output values for varyings, but the other
vendors don't apply these. To properly emulate this we would have to
analyze the shader header. For the time being, apply the same default
Nvidia applies so we get the same behaviour on non-Nvidia drivers.