Inline editing of issue title and description in mobile

• This is already done in desktop.
• But we also want to bring this to mobile, so as to unblock https://gitlab.com/gitlab-org/gitlab-ce/issues/36670.
• The suggested UX design is simply when you tap the existing edit option in the Options dropdown menu, it goes into inline editing mode for the title and description.

Design

Optimized the description field on the small screen:

• The tab bar is in the first line.
• The format style options are in the second line.