Add CollapseVectors to LoweringCompilers

This places the CollapseVectors transform at the head of the
MiddleFirrtlToLowFirrtl transform sequence. InferTypes is added as
types may change due to running CollapseVectors.

This include modifications to ReplSeqMemTests to bring this in line
with the new code generation of CollapseVectors.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>