[compiler] Fix toFastSeq to not copy a WrappedArray or ArraySeq

[patrick-schultz]

Change Description

This had been my intention in the first place. to was correctly avoiding copies in 2.13, but not 2.12. Now we call ArraySeq.from, which we wrote ourselves to avoid copies. This is most useful in the pattern

def foo(args: T*) {
  expectsIndexedSeq(args.toFastSeq)
}

where args is a WrappedArray.

Security Assessment

• This change cannot impact the Hail Batch instance as deployed by Broad Institute in GCP