RN: UI/UX Improvements to the mobile post draft area

Description

This ticket is done on the mattermost-mobile repository

See design: https://projects.invisionapp.com/share/UCTBUSUK5BH#/screens/377642040

QA Test Steps

tested on the PR, ships in 1.26.0

Reporter

None

Mana

None

Assignee

Mattermost Community

QA Assignee

Jelena Gilliam

Reporter

Eric Sethna

Epic Link

None

Fix versions

Mattermost Team

Mobile

Sprint

None

Labels

None

QA Testing Areas

Attachments
Mobile - RN

Components

None
Configure