Outlook Addin JS Object Model - Expose getSharedPropertiesAsync on Office.context.mailbox

In an OWA client, when more than one email is selected in a shared mailbox, Office.context.mailbox.item becomes null preventing access to the only means of retrieval of the shared mailbox properties via Office.context.mailbox.item.getSharedPropertiesAsync

We need a reliable way to retrieve the properties of the current mailbox

Suggestion: expose getSharedPropertiesAsync method on the mailbox object instead of the mailbox.item object like this:

• do this: Office.context.mailbox.getSharedPropertiesAsync()
• instead of this: Office.context.mailbox.item.getSharedPropertiesAsync()

This issue is covered here: https://github.com/OfficeDev/office-js/issues/3989