Add tests for getting tags from FASTQ through chaining Giraffe and into BAM

[adamnovak]

Changelog Entry

To be copied to the draft changelog by merger:

• --comments-as-tags is now under test with vg giraffe's chaining codepath
• Surject tests now test SAM tags in GAM with an actual vg surject command line
• vg surject now preserves unrecognized GAF tags as tags on output alignments (and GAF input in general retains tags)
• vg giraffe chaining mode now properly retains input tags on unmapped reads

Description

There was concern that tags might be falling out on the way from FASTQ to GAM, when Giraffe is using its chaining codepath.

I found some ways that tags could indeed fall off reads (specifically, when a read was unmapped on the chaining codepath, or if we went through GAF format and then vg surject).

This adds tests for those cases and fixes them.

[adamnovak]

This uses vgteam/libvgio#90