[3dtiles] Skip completely transparent primitives

[nyalldawson]

Don't render these in 2d or 3d views

Fixes #55579

[nyalldawson]

@wonder-sk look ok to you?

[qgis-bot]

The backport to release-3_34 failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply 1f2b11cdca9... [3dtiles] Skip completely transparent primitives
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".

stdout

Auto-merging src/3d/qgsgltf3dutils.cpp
CONFLICT (content): Merge conflict in src/3d/qgsgltf3dutils.cpp

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_34 release-3_34
# Navigate to the new working tree
cd .worktrees/backport-release-3_34
# Create a new branch
git switch --create backport-56303-to-release-3_34
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 1f2b11cdca95f2d940eb8d0bd1adba1a5c18a7e6
# Push it to GitHub
git push --set-upstream origin backport-56303-to-release-3_34
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_34

Then, create a pull request where the base branch is release-3_34 and the compare/head branch is backport-56303-to-release-3_34.

[P-SLISSE]

Hi,
If necessary, you can test this evolution with this sample dataset
Testing_3DTilesWithFullTransparency.zip
The file mesh_6180061.b3dm is a mesh with full transparency, that as to be skiped in 2D and 3D cartographic views
Thanks for this upgrade for 3DTiles display in QGis