Enable glTF coordinate conversion for our examples

[janhohenheim]

Objective

• Part of Enable correct glTF coordinate conversion by default #19686
• Implements Port 3D examples to new glTF coordinates #19990
• Followup to Nudge users into migrating to new default glTF coordinate conversion #19816 (that was the controversial one!)
• Since Nudge users into migrating to new default glTF coordinate conversion #19816, all of our examples loading a glTF show a deprecation warning because we don't use the fixed coordinate system conversion internally yet

Solution

• Let's enable the new coordinate system conversion as part of [dev-dependencies] and port all of our examples!
• The course of action was selected on a case by case basis
  • Sometimes, the environment map used for decorative lighting or the background would be flipped. That doesn't matter at all for the example, so I allowed the slight visual change.
  • Sometimes, nothing needed to be changed. A model would be flipped, but the example looked just as good and conveyed the same information, so no need to touch it.
  • Sometimes, a model was clearly meant to face the camera. For nearly all cases, I rotated the model to face the camera, as keeping the camera positioned the "usual way" seems like the most idiomatic choice
    • For mixed_lighting, that would intrude on other code that assumed that the Transform of the mesh was equal to its GlobalTransform, so I rotated the camera instead
    • For the scene viewer, it seemed more logical to import the scenes as-is and rotate the camera instead to face them
    • reflection_probes required a bit of an ugly fix, but this one is undergoing a major change in its cubemaps anyways in an upcoming PR, so no need to touch it here. See Environment Map Filtering GPU pipeline #19076. That PR will make it nicer again :)
• I also fixed an issue where glTF lights were rotated the wrong way that I discovered while porting
  • I verified that this light handling is correct with a dedicated Blender test scene not included in this PR
• Notable corollary: meshlets are now more different from glTF assets, as they use Bevy's coordinate system, not glTF's
  • Jasmine says this is the correct behavior

Testing

• I went through all 84 instances of the regex \.gl(tf|b) in the examples directory and compared them all with their output without the new feature

[janhohenheim]

Marking as uncontroversial because

• This migration path is the one that Cart favored
• The controversial part was already merged (i.e. showing the migration warning)
• We obviously don't want to have examples with deprecated code in them

[mate-h]

The whole diff looks good to me, I have no nitpicks about it. I tried converting some assets to use this new coordinate system but determined that would take too much effort to be in scope of this PR. Thus, we will do it incrementally on an example-by-example basis instead.
I spot checked a couple of examples (specifically where baked lighting direction matters), maybe we can check pixel eagle and see what remaining examples pixel output have changed.

[janhohenheim]

Update: some important discussion https://discord.com/channels/691052431525675048/743663924229963868/1394079989552644186

[janhohenheim]

Reopening since the community vibe seems to be that these changes are still the best way forward, but we should document it better: #20121
Still leaving this as uncontroversial because the controversial bit was #19816, not this followup