Fixes needed to support Scala 2.13

[sifive-benjamin-morse]

DRAFT

Fixes needed to support Scala 2.13
Mostly need .toSeq on mutable Seqs
A few import resolution, was pickup wrong Utils.
Fixed Seq problem returned in tuple

Related PRs / Issues

UI / API Impact

Verilog / AGFI Compatibility

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[davidbiancolin]

The changes themselves look good.