#363: Tweak logic for artifactLocation.artifactIndex

Luke pointed out that the description of the logic for when
artifactLocation.artifactIndex  is required was missing a case: the case when the  artifactLocation  object is contained by an  artifact  object. I added the missing case, and rearranged and (I hope) clarified the rest of the logic.

Here is the change draft:

https://github.com/oasis-tcs/sarif-spec/blob/master/Documents/ChangeDrafts/Accepted/sarif-v2.0-issue-363-artifactLocation-index.docx

The changes are in §3.4.5, “artifactLocation.artifactIndex property”.

The important sentence is:

If
thisObject  occurs as the  artifactLocation  property (§3.23.2) of an  artifact  object in
theRun.artifacts , then  artifactIndex
MAY  be present. If present, it  SHALL  equal the array index within
theRun.artifacts  of the containing  artifact  object.

Here is the up-to-date provisional draft:

https://github.com/oasis-tcs/sarif-spec/blob/master/Documents/ProvisionalDrafts/sarif-v2.0-csd02-provisional.docx

Thanks,
Larry