Feedback: Moving Editor Mode Switcher to Bottom Row

Note: Please provide feedback in the comment section of this Issue.

In %16.2 we have introduced a new layout and UI for the Markdown and Rich Text Editor via the following MR.

What does this MR do and why?

Changes editor layout to address the two biggest feedback aspects:

Preview button being out of reach
Limited available space still being a problem

To fix that, we will make the following changes:

Moving editor mode switcher into bottom row
Converting "Supports markdown" text into an icon
Remove "For quick actions type /" and instead add a "Quick actions" button in the toolbar

Constraints

The Rich Text Editor is not yet available in all places. The plan is to have it available everywhere soon and we are actively working on that. Until then we need to find a design that works for all cases, but our focus is to have the best possible design for when the Rich Text editor is enabled, as the current plan is to toggle the feature flag in the next 2-3 milestones.

This new layout also doesn't completely fix the space problem, our long-term plan to deal with that is to combine multiple buttons into one dropdown button for smaller viewports.