Description:
This is related to #44, however, while that issue in particular asks for multiple JDKs to be installed with a single setup-java invocation, I would like the general setup-java invocation to provide a Maven Toolchains declaration for the selected JDK(s).

This requires putting a toolchains.xml file with the proper definitions into the $HOME/.m2 location of the current user, i.e. the one running Maven.

Implementation of #44 would require changes to this, i.e. all additional JDKs would have to be correctly exposed in the toolchains declaration as well.

Justification:
This would allow using setup-java with less overhead in projects that have Maven toolchain requirements configured and also allow Gradle to pick up JDK locations automatically starting with 7.4. This was something discussed in #44 as well and is to be implemented in gradle/gradle#14903 with a different solution.

Are you willing to submit a PR?
There's a pull request: #282