Add KTX2 docs

[elalish]

Thanks to @donmccurdy we now have support for KTX2 textures, both in and out of glTF. This is just adding documentation (largely copied from the BasisTextureLoader docs).

It also includes a small update to the .d.ts file for KTX2Loader, so it might be nice to include this in the next point release, @mrdoob.

[donmccurdy]

Might be good to include a copy of KTX2Loader.html in the zh/ folder as well, it can be translated later. Otherwise looks good!

[mrdoob]

Thanks!

[Mugen87]

Notice this PR targeted the master branch. #21168, too.

[mrdoob]

Yep, changed it myself. This requires a point release.

[Mugen87]

BTW: Is there a way to prevent PRs targeting master?

[mrdoob]

Well, maybe this one was not required for the point release, but while I was at it... 😇

[mrdoob]

BTW: Is there a way to prevent PRs targeting master?

I do not know, I wish there was a way. But at the same time, I wouldn't want to lose the flexibility.

[Mugen87]

Ah okay! I was not aware you have changed the branch^^.

[mrdoob]

Yeah, I was trying to push 0.125.2 to npm without the other changes in dev.

I think I did it correctly but somehow I ended up merging master and dev afterwards?

Anyway, should be good now I think🤞

[mrdoob]

Oh, I see what I did. I didn't think this was built on top of the latests in dev. I should have cherry-picked instead...

Anyway, I'm a git-noob still 😁

[ozoneuniverse]

Amazing momentum Everyone! Cheers! and Thank you!