Add new status for support threads: "awaiting user's verification for resolution"

[Daedalon]

Migrating from ​#wp24536:

WordPress.org support threads are currently often left by users in "not resolved" state even when commenting that the issue is fixed. "[ ] Mark this thread as resolved" below the comment box is not noticeable enough.

A new status should be added: "awaiting user's verification for resolution". This would be set by plugin support team members when they're providing user with an answer that is expected to solve the issue.

The comment box would then require the original poster to either accept or reject the resolution. The submission button would not be clickable before either one is selected.

The email notification that the original poster receives would also contain a request for action with links to either accept or reject the resolution. These would lead to the comment form that has the appropriate option selected.

comment 1:

Replying to Daedalon:

This reduces the time plugin authors spend in manually setting tickets resolved after users confirm the resolution but forget to set the status. The less time spent on support bureaucracy, the more time spent on development and the stronger the WordPress ecosystem.

Worth discussion with the support team.

[SergeyBiryukov]

#1343 was marked as a duplicate.

[tferry]

+1 to this. Seems tidier to me and helps separate out "silently resolved" topics from genuinely unresolved ones.

[Clorith]

The introduction of new statuses like this feels much more like a ticketing-move, than a forum related one.

Users are also likely to get their reply via email notifications, and won't jump back on the forum for that specific issue.

It should be noted that plugin (and eventually theme) authors and representatives can mark threads in their own forums as resolved.

Fixes #165

### Screenshots

#### Mobile
| Before | After |

|

| | |

#### Desktop
| Before | After |

|

| | |

### How to test the changes in this Pull Request:

1. Build the styles
2. Ensure you have an /enterprise-2 page and run it
3. Add dir="rtl" to the HTML element
4. Check that layout looks ok

Note: the CTA arrow styling of 'Try WordPress' had not been fixed in this PR as it is inherited from the parent theme, new issue raised there: ​https://github.com/WordPress/wporg-parent-2021/issues/68