Add agmFitBounds to AgmPolylinePoint

[johnheroy]

Issue description
It looks like the agmFitBounds directive only works for AdmMarker but not AdmPolylinePoint, this would be helpful for map components which just render polylines.

[terencehonles]

@doom777 once we get #1704 and #1648 merged in I'll hopefully have some time to look at this. I noticed this was missing and worked around it in our application, but this is something I may be able to contribute in the future. (I'd like to get the others PRs merged in first though, and I'll update #1648 when we get #1704 in)

[loremaps]

Would agm-circle be consider as well?

@loremaps you can write it up, and make a PR

[loremaps]

I gave it a shot for agm-polyline-point...but for agm-circle I am not sure if the whole circle should fit or the just the center 🤔 What do you guys think?

Whole circle