frontend: Implement HealthCheck service

[Warchamp7]

Description

• Adds a new HealthCheckService and associated classes.
• Refactors Idian widgetry for better flexibility.
• Adds some new generic UI widgets.
• Adds widgetry for the display of HealthCheckService info
• Hooks up the Missing Files state to this new system to start

New widgets

Example image. Only Missing Files is implemented by this PR.

Motivation and Context

Currently we do not have a good way to surface information to users about configuration problems or other OBS 'System Health' issues. Often these warnings are part of startup, adding to an already large pile of dialogs and popups we can potentially spawn. In other cases, they are specific to particular settings themselves and only visible when the settings window is open and you are looking at the specific section or actual option.

This system aims to be for configuration warnings or problems which can be resolved, in contrast to a notification system.

I would appreciate feedback from people testing, as well as suggestions for which other settings issues or configuration might be good candidates to be added here.

How Has This Been Tested?

Created some test health items locally, as well as hooked up the scene collection missing files dialog to this system.

Expected behaviour is that Critical items will show in the list first, and fixed items will disappear.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.