Mattermost-server: User autocomplete should match on spaces

[mattermod]

This feature was implemented on webapp and merged for 5.20 but not on mobile RN.
Webapp: https://mattermost.atlassian.net/browse/MM-19761, https://github.com/mattermost/mattermost-webapp/pull/4504

Expected: Allow user autocomplete to match on terms with spaces. For example: “@firstName lastName”, similar to how channel autocomplete works (can be tested by typing ~ followed by a channel name with spaces).

Expected behavior is that once autocomplete is triggered with @, as long as there is a matching entry the autocomplete stays open, if no matching entries then the autocomplete dismisses. Autocomplete is also closed with the Android back button, when the keyboard is dismissed, or an autocomplete entry is selected.

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JIRA: https://mattermost.atlassian.net/browse/MM-22366

[ChrisDobby]

I'll take this if that's OK?

[enahum]

@ChrisDobby any progress on this? do you need help?

[edtrist]

Happy to take a look at this :)