Move benchmarks into big folder
The benchmarks need a longer time to run, so we might not want to run them in every push for our CI. If they are placed in the big folder they are only run if you supply the --all-exec-tests flag to mjtest.
This merge requests also renames the java files to input.java, so that the supplied inputc files are actually read.
It also provides output files for all tests as running the BigTensorProduct test with Java to calculate the reference output leads to a OutOfMemory error on our CI machine.