Position based transcript search to be added to genes to transcript endpoint

[John-F-Wagstaff]

Is your feature request related to a problem? Please describe.
Currently we are lacking a good API endpoint for handling large deletions in particular, since hgvs does not have a currently valid way to describe deletions that exceed the span of the transcript.

Describe the solution you'd like
It has been suggested that this would work well if added to the existing genes to transcript endpoint, and this seems feasible.

Additional context
This needs some tweaks to vvhgvs first, as well as to VV.