Bug Report

Priorities and help requested (not applicable if asking question):

Are you willing to submit a PR to fix? Already done, see #3951

Requested priority: Normal

Products/sites affected: VSTS

Describe the issue:

CommandBar items need to have aria-setsize and aria-posinset so that Narrator will announce their positions within the set.

Actual behavior:

They don't have these attributes

Expected behavior:

They have these attributes.