This Pull Request overrides #2288.
It changes the following:
- Updates dependencies to use Unicode 15
- Updates the boa_unicode crate to use Unicode 15
It's still waiting on the unicode-general-category 0.6 release, which was tagged 3 days ago: 15e7e3182f
The main idea behind this is to upgrade the Unicode version from 13 to 14. I also upgraded the rest of the dependencies, so this closes#1802, #1800 and #1799.