Add support for accessibility profiles

[micahmo]

Pull Request Description

This PR adds support for accessibility profiles. An accessibility profile is a list of settings and suggested values. Applying the profile will toggle the settings to the suggested values. Note that applying a profile doesn't lock you in to those settings; you may still manually set anything. Also the profile can be applied any time or any number of times. It is essentially just a "baseline".

In the UI, each profile displays a description (why one might want to use this profile) as well as a list of the settings and values.

Once the framework is in place, it will be very easy to add new profiles (you essentially just create a widget, and pass the list of settings and desired values), and we can solicit these from the community. To start, this PR intoduces one initial profile for Screen Readers with the settings suggested in #778.

Technical note: Currently only boolean-based settings are supported as part of a profile, but I don't think it would be hard to add others. Just something to keep in mind.

@shortwavesurfer2009 Can you take a look and let us know if this is what you had in mind based on our discussion?

Issue Being Fixed

Issue Number: #778

Screenshots / Recordings

qemu-system-x86_64_Rs4211haPy.mp4

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[shortwavesurfer2009]

Looks good from what i can see

[hjiangsu]

Looks good to me, just some discussion points that I wanted to bring up!