[Packer] Updated the Next State Logic of Iterative Re-Packing

The packer iteratively re-packs the netlist if it fails to create a
dense enough packing. The way it does this can be thought of like
states, where each state turns on a new set of packer options that can
create a denser clustering.

The prior state transition logic for the iterative re-packing did not
turn on enough options to make the clustering as dense as VTR can
manage. This updates the state transition logic to create even more
dense clusterings.

The next state logic is as follows:
- If there is an over-utilized block type, turn on unrelated clustering
  and balanced block type utilization if able.
- If there are overfilled floorplan regions, create more attraction
  groups than the prior iteration (or increase the pull). If all regions
have attraction groups and the pull is strong, do not increase further.
- Finally, if all else fails, increase the target external pin
  utilization if any of the overfilled block types have target pin
utilizations less than 1.0.
- If all prior fails, fail hard.

Found that for the Z1000 architecture, this increased the maximum LUT
utilization from around 68% to around 86%.

Author: AlexandreSinger