[Sdb] Ignore hidden sequence points

Hidden sequence points are created by Roslyn or csc.exe + pdb2mdb...
We could stop emitting them in pdb2mdb and Roslyn but prefer to do this in runtime for two reasons:
* We would need to worry about syncing modified pdb2mdb with runtime
* Maybe we will want to use this hidden sequence points in future inside Runtime and we will have to modify pdb2mdb again...
This is a linear search. How big is this hidden array for a large assembly?