Change how camera intrinsics are used for creation and update

[jtigue-bdai]

Description

This PR changes how the camera intrinsic matrix:

• Is used to create usd cameras
• Is updated from usd camera parameters

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[jtigue-bdai]

@pascal-roth here is that camera intrinsic PR I was talking about.

[pascal-roth]

Good job to remove the code duplication.

I don't know if the focal length of 1/width is a common standard in the literature. What is your source for that? Otherwise, picking that as a default seems a bit arbitrary.

[pascal-roth]

This is not the case, isn't it? The focal_length is not set over the intrinsic matrix but just over the width. We should rephrase that to prevent confusion