Java 15 does not contain javax.annotations

[collinsmith]

Need to add https://mvnrepository.com/artifact/javax.annotation/javax.annotation-api/1.3.2 as a dependency for riiablo:core in order for builds to work. I'm pretty sure this worked before with <13, so maybe this is a newer change. Java 16 is incompatible with current version of gradle so cannot test.

[collinsmith]

Added dependency and was able to compile, need to validate that the dependency propagates across projects correctly (in correct place in the build scripts).

See 508f08d

[collinsmith]

Was apart of Java EE, removed in JDK 11, resolution is to use javax.annotation:javax.annotation-api as I've been
https://www.oracle.com/java/technologies/javase/11-relnote-issues.html#JDK-8190378