Docs: Update logarithmicDepthBuffer with performance caveat

[gkjohnson]

See #17384 and #17384 (comment)

I'm not sure if people feel it's important to include an inline comment about the need for gl_FragDepth like there used to be but at least the docs should note it.

[mrdoob]

Hmm... The note is a bit too mysterious.
Would it be hard to explain what these certain rendering optimizations are?

[gkjohnson]

Would it be hard to explain what these certain rendering optimizations are?

Nope! How does this sound:

Note that this setting uses gl_FragDepth if available which disables the Early Fragment Test rendering optimization and can cause a decrease in performance.

[mrdoob]

Much better! 😀

[gkjohnson]

Updated!

[mrdoob]

Thanks!