Update app dependencies

[pyby]

Description

Update demo and test app dependencies.

Changes made

• Update Letterbox dependency for demo app.
• Update SRGAppearance dependency for test app.
• Update Xcode projects.

Checklist

• The branch should be rebased onto the develop branch for whole tests.
• [x] APIs have been properly documented (if relevant).
• [x] The documentation has been updated (if relevant).
• [x] New unit tests have been written (if relevant).
• [x] All UserObjectTestCase tests has passed successfully locally, included flacky disabled ones.
• [x] The demo has been updated (if relevant).
• [x] Issues are linked to the PR, if any.