Update to gulp 5

[ggetz]

Description

Update to gulp 5.

This is opened as a draft because, while tasks are running, there's still problems. Right now, mainly with the tests.

• Bump gulp version
• Remove outdated stream-to-promise in favor of the native finished
• Remove merge-stream, which does not appear to be maintained. The functionality can be replicated with the gulp API anyway.
• Rearranged some sequential globs to ensure we're working with the new standard
• Passed encoding: false whenever sourcing images or other binary files

Issue number and link

Fixes https://github.com/CesiumGS/cesium/issues/10919

Testing plan

1. Ensure make-zip, build-apps, and start task work
2. Ensure test and test-release pass
3. Unzip release file
4. Confirm release sandcastle and viewer app are unchanged

Author checklist

• [x] I have submitted a Contributor License Agreement
• [x] I have added my name to CONTRIBUTORS.md
• [ ] ~I have updated CHANGES.md with a short summary of my change~
• [ ] ~I have added or updated unit tests to ensure consistent code coverage~
• [ ] ~I have update the inline documentation, and included code examples where relevant~
• [x] I have performed a self-review of my code

[github-actions[bot]]

Thank you for the pull request, @ggetz!

:white_check_mark: We can confirm we have a CLA on file for you.

[ggetz]

@jjspace Could you please review? The goal would be to get this in sometime this week to ensure it has some time in main before the release.

[ggetz]

Thanks @jjspace! All your feedback should now be addressed.