[TODO] Drop C++14 support and make C++17 default

[syoyo]

C++17 is widely supported in compilers as of 2025, and tinyusdz can be compiled with C++17.
One reason staying with C++14 in tinyusdz is for python binding(manylinux_2_24), but we can deprecate manylinux_2_24 as time passes(Guess its ready to migrate to C++17 as default in 2026)

[github-actions]

This issue is stale because it has been open for 30 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 14 days since being marked as stale.

[syoyo]

We plan to release new TinyUSDZ version in early 2026, and manylinux_2_24(C++14) has been deprecated now, and manylinux2014 as of Oct/2025 supports C++17(gcc 9.3), so we'll migrate to use C++17 in the 2026 release!