Dropdown actions for message

Problem/Motivation

"Individual message edit/delete/etc." ( ✨ Message editing Active ) needs dropdown actions functionality for the message.

Proposed resolution

Available options:

• Custom HTML/JS/CSS
• Bootstrap library would be convenient, but feature has to work with any theme.
• "Contextual Links" module
• "Operations" form element.

Selected option: Custom HTML/JS/CSS
Because 'contextual links' and 'operations' only support links, but chat is a form with submit buttons.
So custom solution will enable to use buttons for each operation.

Remaining tasks

User interface changes

API changes

Data model changes