Expand E026 (Invalid vehicle position) for (0,0)

[barbeau]

Summary:

Invalid locations of (0,0) for a vehicle position are relatively common, so we should check for these in E026.

Also consider additional measures for validating location as discussed for GTFS stops in https://github.com/MobilityData/gtfs-validator/issues/148.

Steps to reproduce:

Validate a feed with vehicle positions of (0,0)

Expected behavior:

Throw an error

Observed behavior:

No errors are thrown