Explore use of Java Vector API for SIMD support

[headius]

Inspired by @samyron's work in #730, I'd like to explore the potential of Java's Vector API in Psych.

https://openjdk.org/jeps/489

The API has been gestating for many years, but can be enabled and used on all recent JDKs. The potential here is to get SIMD performance without having to write platform-specific code, and enable it only when the Vector API is enabled at the JVM level.

This could also be a fun project for someone else who wants to play with truly bleeding-edge JVM features and help out JRuby at the same time.

I would love to hear from @samyron about more ideas for SIMD optimization of Psych, and try to implement as many of those ideas as possible in the JRuby extension.

[samyron]

I'm happy to take a look. I haven't looked at the Java Vector API. However, it might be easier to implement similar ideas as to what I did in #730 as the JVM will handle CPU/ISA detection.