DLSSNR: add automatic exposure, extended Trim range and Trim Anchors

[mattjaas]

Summary

This PR adds automatic exposure support to DLSS-NR, significantly extends the available Trim range for the game's own exposure, and adds Trim Anchor Points for precise scene-dependent fine-tuning.

Motivation

A dynamically changing White Point is important for maintaining consistent DLSS-NR image quality across scenes with very different lighting conditions. In practice, many games do not provide an exposure resource that OptiScaler can use, leaving DLSS-NR without a usable dynamic White Point.

The new Automatic exposure mode addresses this by calculating exposure directly from the original linear HDR image. Based on testing across several games, a 5x Trim proved to be a useful starting point for this calculated exposure, so Automatic exposure now defaults to 5x Trim.

This default applies only to Automatic exposure. The game's own exposure still defaults to 1x Trim.

There is also another problem with game-provided exposure: its scale can vary significantly between games and sometimes the values are much lower than expected.

One example is Marvel's Spider-Man Remastered. When XeSS is replaced with DLSS through OptiScaler, the game's exposure becomes available to OptiScaler, but the reported exposure is low enough that achieving the desired DLSS-NR White Point can require a relatively large Trim multiplier.

For cases like this, this PR significantly increases the available Trim range for the game's own exposure instead of assuming that values close to 1x will always be sufficient.

Trim Anchor Points

A single fixed Trim value may still not be enough to maintain the desired DLSS-NR result across the full lighting range of a game. A value that works well in bright outdoor scenes may not be optimal in dark interiors, or vice versa.

To address this, both:

• The game's own exposure
• Automatic exposure

can optionally use Trim Anchor Points.

Each Anchor Point associates the current Base White Point with a selected Trim value. With multiple Anchor Points, Trim is interpolated between them as exposure changes.

This allows much more precise fine-tuning while keeping the White Point dynamic, making it possible to preserve good DLSS-NR image quality in both highlights and shadows without relying on a single compromise Trim value.

If no Anchor Points are configured, the normal Trim slider is used exactly as before.