video_core: sharpen the temporal DLSS stand-in

Fire Emblem: Fortune's Weave's DLSS input matches Eden's (same 720p
image, same detail), but the stand-in's 1440p output was blurrier than a
plain bilinear 2x of it (Laplacian 0.0066 vs 0.0081; Eden's real DLSS
0.0111), and the image drifted darker over time:

- the sample kernel was about twice too wide for the output resolution;
- the history was kept in the output's B10G11R11 format, whose 5-6 bit
  mantissas round away a frame's 0.03-0.1 share;
- the 1-sigma neighbourhood clip removed detail that only some jitter
  positions sample (railings, thin edges).

The history is now an RGBA16F pair the shader writes as a storage image,
with no per-frame copy. Still pixels use a third of the kernel width and
a 1.5-sigma clip, so detail from many jitter positions accumulates.
Moving pixels keep the old kernel and 1-sigma clip, and so do pixels
that moved recently or whose history falls far outside the
neighbourhood (content that changes without motion vectors), remembered
in the history's alpha. Static output goes from 0.0066 to 0.0102 with
no brightness drift and no new ghosting.

With resolution scaling the stand-in used to fall back to a bilinear
blit. The images are now scaled up as BlitImage does, the jitter is
scaled to host pixels and the history follows the framebuffer's render
area.

RCAS (temporal_sharpen.frag) sharpens a copy of each result, never the
history, in range-compressed space since the output is HDR. Its strength
is the sharpness slider, relabelled "RCAS Sharpness" (0% turns it off).
EDEN_NX2_TEMPORAL_KERNEL, _CLIP, _KERNEL_MOTION, _CLIP_MOTION and
_WEIGHT tune the filter (all four filter values at 1 give the old one),
and EDEN_NX2_TEMPORAL_SHARPEN=<stops>|off overrides the slider.

Assisted-by: Claude Opus 5.5 (debugging, implementation and drafting)
Signed-off-by: Duck912 <350528965+Duck912@users.noreply.github.com>

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