Remove PlacerMoveContext

[soheilshahrouz]

PlacerMoveContext class contained bounding-box information for clustered nets, some scratchpad vectors, and first_rlim. This PR moves all bounding-box related info to NetCostHandler. Scratchpad vectors are moved to classes that use them, and first_rlim is now a static data member of MoveGenerator.

[amin1377]

Thanks, Soheil! Overall, the PR looks good. I just left a few minor comments. Also, since you're modifying some performance-critical parts of the code, I'd suggest running the Titan benchmark on the SAVI machine and comparing its runtime against the master branch to ensure there are no significant regressions.

[soheilshahrouz]

Results for VTR benchmarks

Metric	master	feature
vtr_flow_elapsed_time	1	0.9956233242
parmys_synth_time	1	0.9984187005
abc_depth	1	1
abc_synth_time	1	0.9992354382
num_clb	1	1
num_memories	1	1
num_mult	1	1
max_vpr_mem	1	1.001330976
num_pre_packed_blocks	1	1
num_post_packed_blocks	1	1
device_grid_tiles	1	1
pack_time	1	0.9930076
placed_wirelength_est	1	1
place_time	1	1.010553331
placed_CPD_est	1	1
min_chan_width	1	1
routed_wirelength	1	1
min_chan_width_route_time	1	0.9870603223
crit_path_routed_wirelength	1	1
critical_path_delay	1	1
geomean_nonvirtual_intradomain_critical_path_delay	1	1
crit_path_route_time	1	1.008222132

[amin1377]

Thanks!