[AP][InitialPlacement] Created Isolated AP Flow

The old Initial Placer used in the AP flow was constructed within the
initial placer of the non-AP flow. This forced the AP flow to try to
place blocks one at a time with minimum displacement. This is non-ideal
since blocks that were placed earlier were being getting first picks at
locations, which may displace a future cluster which may be a better fit
for that location.

Separated out the AP initial placement code. For AP, initial placement
is done in passes.

The first pass will try to place clusters exactly at the tile that the
centroid of all atoms within the cluster want to be placed (according to
the global placement). Any clusters that could not be placed are
reserved for the next pass.

The second pass will allow clusters to be placed within 1 tile of their
centroid.

All subsequent passes will allow cluster to be placed exponentially
farther from their centroid.

The initial placement terminates when all clusters have been placed or
if the max displacement is the size of the entire device.

The clusters are sorted based on the size of the macro that contains
them and the variance of the placement of the atoms within the macro.
This allows large macro blocks with low variance to be placed first.

Author: AlexandreSinger