This change allows transcoding new UASTC .basis files to BPTC which
results in much higher quality compared to UASTC -> BC3 transcoding.

The change needs to introduce BPTC support to three.js core for this to
work; the format is introduced in EXT_texture_compression_bptc which is
available in Chrome Canary on Windows (and possibly elsewhere?)

The update to Basis transcoder just pulls it directly from Binomial
repository; the transcoder is a bit larger now, unfortunately, because
it needs to support UASTC.

Note that we use mode 5 unconditionally to make sure RGB and RGBA
textures work.

BPTC (BC7) and BC3 are the same size in memory so this shouldn't
negatively impact VRAM consumption.

Instead of assuming a worst case when the weight of each target is +-1,
assume that the sum of the weights is +-1 instead.

This isn't quite correct and may result in a bounding box that's too
small, but in at least one case - when morph targets are used for
keyframe animations and only two are active at a time - this results in
a much smaller bounding box.

In some other more realistic cases this may also reduce the bounding box
without a real impact on it being conservative, e.g. it's common to have
50 blend shapes for facial animations but only a few are active at a
time, and extreme deformations are typically contained within a box
that's computed with the new algorithm as well.

Fixes #18809.

depthTest is kept enabled since it may be desirable to render the sky after other geometry is already rendered.

This reverts commit 15947a3a.

1. Function `processMesh` has 2 `cacheKey` variables: one for mesh and one for attribute. Because of that meshes are cached with invalid keys. This PR renames first `cacheKey` to `meshCacheKey`
2. Fix multimaterial mesh caching by joining uuids