Improve JQL search page for user identification

Issue Summary

Since the implementation of the GDPR and with the deprecation of usernames some features haven't been fully adapted.  This is the case of the Advanced Search Page, where the accountId is now the preferred value when you search for a user. 
Show the username/email in a tooltip or enhance this behaviour for users having Browse User and groups Global permission when you enter or select a user.

Steps to Reproduce

1. Go to the Advanced Search page
2. Add some users as a search criterion and switch to Advanced Search JQL.
3. It translates into accoutIDs
4. On this JQL, it is not possible to know who is the user on each accountId.

Expected Results

If the GDPR forbids to save the filter with email or usernames, implement a tooltip or mechanism to identify the users.
It is needed because old values in comments, issue history are marked with the Username, making very difficult to identify users. Gadgets, filters require usernames but there is no direct way to get them.

Actual Results

Only AccountIDs are shown in JQL advanced search without a clue to know who is the user.

Workaround

Create a temporary filter and test every single user accountId.
Being site-admin to access user page section