Added the toastui WYSIWYG editor to the frontend

This makes visual reviews work with private/internal projects.
This also has added benefit of using the user's GitLab username
and email.

Migrated GlNewButton to GlButton:
- Renamed occurrences of GlNewButton to GlButton
- Renamed occurrences of gl-new-button to gl-button

- Renamed all instances of GlButton to GlDeprecatedButton
- Renamed all instance of gl-button to gl-deprecated-button

Due to switching to the [`auto` strategy in renovatebot][1].

[1]: https://gitlab.com/gitlab-org/frontend/renovate-gitlab-bot/-/merge_requests/141

With 5000 chars as a hard limit, there are many cases where we'd want
to render individual mermaid diagrams. With this we're adding a render
button which will render the nearest mermaid svg.

These are the FE changes that anticipate a parameter from the BE (in a
following commit)

Indicate how many labels are selected

When the user selects more than 10 labels
we should display how many labels are currently
selected and what the maximum is

Cleaned up tests

Fix alignment of label checkmarks

Display selected number of labels at all times

Disable selection of new labels
after max labels selected