[3.x] Fix GLTF light import

[aaronfranke]

This fixes a regression (#53019) from the changes to the GLTF module in #34193 which were then backported to 3.x. I'm making the 3.x PR first since the same numbers in the master branch produce different visuals, so I'll have to tweak those. This PR also adds documentation to the GLTFLight class. master version: #53109

For the record, here's why these values are the way they are. GLTF lights with no range specified behave like physical lights which have infinite range, so we default to INFINITY for the range (but this is later clamped to 4096 if making a node). For the color, default to white, which is the most sensible option, otherwise we'd have black lights by default, which do not lighten things. For the intensity, default to 1.0, since 0.0 means no light. For the spotlight angle, default to an eighth turn (on both sides, so the cone's edges are a quarter turn apart), rather than 0.0, which would mean the spotlight is emitting light in an area of zero size.

[fire]

Test failure. Oh no.

[aaronfranke]

@fire It's just doc changes (which is why I didn't see it until posting the PR). Patience, I'm working on it.

[fire]

Test strategy:

Open lights in expected Godot Engine version.

Post before and after shot. I expect like a black vs lit scene or something.

Let me know if you can think of others.

[fire]

Lights show as expected.

[akien-mga]

Thanks!