Make probe count adjustable to better accomodate low VRAM scenarios

[Geenz]

This is intended to better wrangle probe memory usage, for example on low-mid machines and the rare low potato that can handle smaller numbers of probes.

During V7's development we disabled this as it was more or less determined that decreasing probe count was dubious at best in terms of performance. However, VRAM savings can be had on lower spec GPUs and integrated GPUs that rely on shared memory which something like this can have a significant impact.

Test Plan

• Modify the maximum probe count (debug setting RenderReflectionProbeCount)
• Open the texture console and note memory usage changing with maximum probe count. Higher probe counts should see more memory, lower probe counts should see less.
• Change the quality preset to Low+ and note the VRAM usage as a baseline.
• Increase the quality preset to Ultra - the VRAM usage should have increased (as denoted by the estimated free VRAM)