Convert masquerade UI widgets to Function Components + TypeScript

[bradenmacdonald]

The masquerade UI widget:

... is using old-fashioned class-based components and JavaScript. In this PR I have modernized it, converting it to TypeScript and Function Components.

There should be no changes to the functionality, but the code should be much easier to understand.

[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald!

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