Change the query compare command's text based on how many items are selected

[aeisenberg]

The workflow for comparing queries is different if you have one query selected or two. When one query is selected, and a user invokes the compare command, an options box opens where the second query can be selected. When two queries are selected, the comparison happens immediately.

We should either:

1. use two commands for these two workflows and only display one or the other based on selection count. This is currently blocked by Enablement using listDoubleSelection and listMultiSelection not working in contributed view microsoft/vscode#99767
2. Change the command title text based on the number of items selected. Not sure exactly how best to do this.

When one item is selected, use Compare with... and when two are selected, Compare Selected.

[aeisenberg]

Option 3: Just use "Compare Results" in all cases.

[yoff]

At least until the block is removed, option 3 seems excellent. After that, it would be nice to standardise.

[jcreedcmu]

A proposal @dbartol made for how to achieve 2 (assuming I'm reproducing it correctly here!) is to dynamically change the viewItem field of all query history items every time the selection changes, and to use "when": "... viewItem == ..." restrictions in package.json to selectively show the right command at the right time.

This would probably work ok except that it is complicated by the fact that we're already using .viewItem = "interpretedResultsItem" to keep track of which query history items have interpreted results, to control visibility of the "View Sarif" command. I think we should probably keep our use of viewItem to properties that genuinely to vary from item to item.