[Feature] Image sampler interpolation

[astrsh]

Pre-Request Checklist

• I have checked that I am on the latest version of Terra.
• I have searched github for similar features requests, including closed
  ones, and found none.
• I believe this is within the scope of Terra.
• This feature request is for all of Terra, and isn't something that
  should be implemented by a pack or addon.

Feature Description

Add a interpolation key to the IMAGE sampler.

What Problem Does This Solve?

With frequencies below 1.0, outputs from image samplers become pixelated. For things distributed on a very large scale (e.g continents), config devs would have to use a very large image to avoid pixelation, which may not be ideal if the scales are on the magnitude of thousands of blocks.

A Solution You'd Like

Allow an option for interpolation to be applied for upscaled images. This could be applied at load time so interpolation isn't calculated at runtime, or calculated at runtime if memory is a concern

Alternative Solutions

Config devs could upscale the images themselves, this just provides another more convenient option.

[nihiluis]

Would be super useful. I assume that upscaling the image yourself significantly decreases image editor performance (while painting, for example in GIMP) and also requires additional RAM at runtime if 1:1 detail is not needed.