Deprecate ECal cellxy.txt and use EcalGeometry instead

[tvami]

I am updating ldmx-sw, here are the details.

What are the issues that this addresses?

Resolves #1413

The code certainly got much simpler like this, no weird stepping in the mapsx/mapsy anymore.

Check List

• I successfully compiled ldmx-sw with my developments
• I ran my developments and the following shows that they are successful.

As a test I fixed the X location to -9999, or to -270 --> indeed it shows that it's not fiducial.
Otherwise ran the new kaon config, the fiducial case looked ok too.
I expect the bigger effects to show up in signal, especially with the 1 GeV case.

[tvami]

@tomeichlersmith I think we should cut gold and then have this PR in, like that it nicely separates from other developments (like the lin-reg changes)

[tomeichlersmith]

This is an excellent update and one that a student I'm working with also has a use for!

My only comment is about reducing duplication.

[tomeichlersmith]

Awesome, thank you!

The last thing is just to update the documentation of getID to include the fallible parameter. And maybe an example about how to use it, e.g.

(doxycomments can contain codeblocks just like markdown).

auto id = geometry.getID(x, y, ilayer, true);
if (id.null()) {
  // position (x,y) is not contained within a cell in layer ilayer
}