DRY the constant definitions

[armanbilge]

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We define several constants for JVM in Java files and then again on JS/Native in Scala. I think the Java sources actually produces "less efficient" bytecode on the JVM than on JS/Native, because Scala final vals are directly inlined at each use site. I doubt this makes a difference in practice, but there's no need to maintain two copies of these definitions.

The hardest part of this issue is convincing Daniel S that we aren't trashing performance with this change 😝