UI acceptance tests for sharing with multiple user and groups

[phil-davis]

Add webUI acceptance tests to cover sharing file/folder with combinations of multiple users and groups, and changing the permissions and/or expiration date of 1 or more of the shares.

Include the case when a user and a group have the same name (see issue #36813 )

The latest backend code for all this (fixing... sharing with multiple users/groups and specifying expiration date...) was merged in PR #36766