Fixes hail-is#13346.

Another user was confused by this: hail-is#14102. Unfortunately, the world
appears to have embraced missing values in VCF array fields even though the single element case is
ambiguous. In hail-is#13346, I proposed a scheme by which we can disambiguate many of the cases, but implementing
it ran into challenges because LoadVCF.scala does not expose whether or not an INFO field was a literal
"." or elided entirely from that line.

Anyway, this error message actually points users to the fix. I also changed some method names such that
every method is ArrayType and never TypeArray.