Mattermost-server: RN: Restyle mobile autocomplete

[mattermod]

In line with the work done on https://mattermost.atlassian.net/browse/MM-22956, the following refinements are proposed:

• Removing lines between items in the list to reduce noise (except when dividing sections)
• Updated Category labels style
• Increased size of avatars for @mention or user autocompletes
• Inset the autocomplete popout and reposition so it’s clear it relates to the post draft

NOTE:

This is in conjunction with UI updates to the Desktop as well: MM-22956

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JIRA: https://mattermost.atlassian.net/browse/MM-22968

[avasconcelos114]

I'll take care of this one :)

[esethna]

Hey @avasconcelos114, thanks for taking this! How's it going, need any help here?

[avasconcelos114]

Ah yep, I had slight problems with getting the autocomplete to render on top of the post draft area (in the z-axis), plus been quite busy at work so I sadly haven’t been able to dedicate as much time as I would have liked to sort things out

I’ll probably try to power through it this weekend without sorting the z-index stuff and then resolve that and any other lingering issues during PR reviews :)

[esethna]

Awesome work @avasconcelos114!