Cycles X: Initial support for the constant time rendering

Allows to limit render time, so that rendering will either happen
until all samples are finished, or the given time limit is reached.

Currently is only implemented for background and headless renders,
as those seems to benefit the most. In the viewport would still
like to investigate idea of keeping rendering until desired noise
floor is reached before adding extra settings there.

The usecases for the non-interactive (background, headless) renders
includes:

- Rendering a shot previews for movies.
- Ensuring some "bogus" frames do not stall the render farm.
- Allows to implement benchmark which will work reliable for both
very powerful and weak hardware configurations (as an example,
top-end GPUs and mobile GPUs) without requiring to wait forever
on a non-powerful hardware.

One of the tricky parts which is not solved in this version yet is
support of constant time rendering with multiple big tiles. However,
support of big tiles will be an addition on top of the existing code
as some sort of time limit would need to be enforced for every tile
(in other words, support of constant time render for multiple tiles
will be implemented on a higher level).

Differential Revision: https://developer.blender.org/D11526

Cycles X: Re-arrange sampling panel

More explicit separate viewport from render settings. Makes it easier
and more clear to add settings which are only for preview or only for
the final render.

| Before | After |
| {F10177700} | {F10177701} |

Among other thngs removed unused CYCLES_RENDER_PT_sampling_total.
Think better would be to call draw_samples_info for both viewport
and render samples.

Differential Revision: https://developer.blender.org/D11633

Fix Cycles X shadow catcher artifacts

Were caused by matte object appearing in the division process.

This change makes it so the matte object is removed from the
combined pass before division, which solves artifacts caused
by anti-aliasing (the matte "bleeds" into the shadow catcher
and produces artifacts around the rim).

Additionally made certain parts more explicit and better
documented.

Test file: {F10177353}

| Before | After |
| {F10177355} | {F10177358} |

Differential Revision: https://developer.blender.org/D11632

Cycles X: Implement OptiX denoising of shadow catcher passes

Pretty much follows similar change in the OIDN.

The information about whether denoiser should use fake albedo for a
specific pass is stored in its PassInfo.

It is probably possible to improve performance of the filter_convert_to_rgb
kernel (avoid per-pixel fake albedo check, avoid scaling normal for every
denoising input pass, ...). Not sure it will bring measurable performance
so leaving it for the future development and investigation.

Differential Revision: https://developer.blender.org/D11614

Cycles X: Use RenderBuffer in the denoise task API

No functional changes, but gives possibility to use PassAccessor to get
pixels of the input noisy pass.

Cycles X: Implement float support in PassAccessorGPU

Rather straightforward implementation, with some code-generation
macro which takes care of some boiler plate code.

Unfortunately, clang-format does some weird decision in the
`kernel_as_string ` function. Attempt to disable clang-format via
comment makes the comment to be weirdly indented. So this part
is left-as is.

Similar to the PassAccessorCPU there is no overlays applied to
the float result.

Tested with an upcoming refactor of the OptiX denoiser which
uses pass accessor.

No functional changes so far.

Cycles X: Use pass accessor in the OptiX denoiser

No functional changes, just converging pass accessor to a commonly
used utility.

There is still custom kernel used, which ensures that pixel values
are within expected range.

Fix OptiX denoiser for transparent film in Cycles X

Fix Cycles X shadow catcher display pass

Missed in the previous fix for viewport passes in d9a645dcc02.

Cycles X: Spelling corrections

Got ,missed in patch transition between computers.