Implement errors reporting with error position in expression

[plynchnlm]

(Moved from lhncbc/fhirpath.js, originally by niquola.)

to do this we can collect position for each node during parsing and propogate node to validation places

[brianpos]

@plynchnlm I think this is now implemented and can close this issue?

[yuriy-sedinkin]

I don't see this implemented in fhirpath.js.

[plynchnlm]

I am not sure what errors were in mind. The ANTLR parser reports syntax errors with position information, but he must have known that when raising this issue.