Output missing vcf fields as a single .

[lbergelson]

Description

• Previously vcf genotype fields with a specific number of elements were output as a comma separated list of dots
• This is valid, but uneccessarily long and doesn't provide any additional information.
• Now only a single dot will be emitted.
• ex: .,.,. -> .

This is a follow up to #1371

Checklist

• Code compiles correctly
• New tests covering changes and new functionality
• All tests passing
• Extended the README / documentation, if necessary
• Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1389 into master will increase coverage by 0.195%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1389       +/-   ##
===============================================
+ Coverage     68.023%   68.217%   +0.195%     
- Complexity      8362      8649      +287     
===============================================
  Files            571       571               
  Lines          33877     34415      +538     
  Branches        5662      5869      +207     
===============================================
+ Hits           23044     23477      +433     
- Misses          8644      8715       +71     
- Partials        2189      2223       +34

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/variant/vcf/VCFEncoder.java	86.316% <ø> (-0.619%)	68 <0> (-4)
...java/htsjdk/variant/vcf/VCFCompoundHeaderLine.java	74.83% <0%> (-0.68%)	47% <0%> (-1%)
...main/java/htsjdk/variant/vcf/AbstractVCFCodec.java	76.218% <0%> (+0.573%)	100% <0%> (+2%)	⬆️
...dk/variant/variantcontext/GenotypeLikelihoods.java	85.827% <0%> (+0.856%)	92% <0%> (+18%)	⬆️
...va/htsjdk/tribble/TribbleIndexedFeatureReader.java	71.978% <0%> (+1.648%)	26% <0%> (ø)	⬇️
.../htsjdk/variant/variantcontext/VariantContext.java	80.545% <0%> (+2.831%)	443% <0%> (+197%)	⬆️
...n/java/htsjdk/variant/variantcontext/Genotype.java	62.917% <0%> (+3.881%)	125% <0%> (+45%)	⬆️
...java/htsjdk/variant/variantcontext/CommonInfo.java	53.939% <0%> (+6.076%)	68% <0%> (+21%)	⬆️
src/main/java/htsjdk/variant/vcf/VCFUtils.java	50.532% <0%> (+6.087%)	26% <0%> (+9%)	⬆️