Don't use enormous offset for second log depth frustum near plane.

[kring]

When log depth is enabled, and multiple frustums are still needed, Scene previously made the next near plane overlap the previous one by 10% for opaque rendering (as compared to 0.01% overlap when log depth is disabled) . With the default setup, this is 10 million meters. When a scene has a mix of opaque and translucent objects, 10 million meters of eye-space difference is easily visible as incorrect depth testing. This PR changes log depth to use the same overlap as non-log-depth (0.01%).

Since I have no idea why this was set to 10% in the first place, there's a decent chance this will introduce a bug elsewhere. But multiple frustums are rare with log depth anyway, and any artifacts would be seams between frustums, which I expect to be much less offensive than rubbish depth testing.

This PR also includes a small tweak to how v_depthFromNearPlusOne is calculated that might make it more numerically stable, but I couldn't see a difference either way from it.

Fixes #8725

[cesium-concierge]

Thanks for the pull request @kring!

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[lilleyse]

Thanks @kring

[TJKoury]

Thanks @kring!