Optimize BFS search

[mkurc-ant]

This PR contains few optimizations related to BFS search:

• setBfsInQueue(BfsIndex index, bool value) got replaced by two functions setBfsInQueue(BfsIndex index) and clrBfsInQueue(BfsIndex index). This removes the need for checking the set/clear argument.
• Map is used instead of UnorderedMap for ArrivalMap. Since Map orders keys searching is quicker.

Assessment of introduced changes was done by running OpenROAD-flow-scripts CTS stage (multiple runs) on BlackParrot design with nangate45 PDK locally on an Intel(R) i7-8700 CPU @ 3.20GHz machine. Prior to the modifications the stage took about 248.4 seconds whereas with the modifications around 243.6 seconds