Optimization of offsets for MAXAR_content_geojson string properties

[timoore]

Description

Offsets to string property values were always stored as 64 bit integers. This PR chooses the appropriate size, which can be UINT8, UINT16, UINT32, or UINT64

Issue number or link

#1414

Author checklist

• I have submitted a Contributor License Agreement (only needed once).
• I have done a full self-review of my code.
• I have updated CHANGES.md with a short summary of my change (for user-facing changes).
• I have added or updated unit tests to ensure consistent code coverage as necessary.
• I have updated the documentation as necessary.

Remaining Tasks

Testing plan

Run a client with a MAXAR_content_geojson tileset and verify that string metadata is still coherent.

Reviewer checklist

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• Review and run all parts of the test plan on this branch and verify it matches expectations.
  • If the issue is a bug please make sure you can reproduce the bug in the main branch and then checkout this branch to make sure it actually solved the issue.
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  • Code should follow the C++ Style Guide
• Review the unit tests and make sure there are no missing tests or edge cases.
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[j9liu]

Thanks @timoore! I tried this out in Unreal and confirmed that the string data still returns correctly.

Just a few minor comments before merge.

[j9liu]

Thanks @timoore !