[Java]: Add missing `stateTemplate` field and copy in MappedTermBuffers

A very minor fix. While reading through Aeron's log buffer management code, I noticed that `MappedTermBuffers` initializes state files using the log file template rather than the state file template. In fact, the class lacks a `stateTemplate` field to begin with. I couldn't tell from documentation or `git log` history if this was intentional, but I'm assuming it's a wiring oversight.

This change adds a private `MappedTermBuffers.stateTemplate` field and threads it down to the state file call to `reset`. Aeron compiles and tests cleanly.