Pickers: Convert to css-in-js

[micahgodbolt]

Describe the feature that you would like added
This feature is to convert Pickers as a whole to use mergestyles to take advantage of theming and styling.

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[Vitalius1]

@micahgodbolt looks like we need to bump the priority back. Any idea when we can unblock our work in the fluent project?

[KevinTCoughlin]

At a glance the Pickers look straightforward to convert. However, there are a number of inner components which I believe would need to be converted as well. The inner components' scss seems more involved than their containers.

I commented not to sign-up just yet, but to say that some of these seem like reasonable candidates for devs converting components to css-in-js for the first time.

[Vitalius1]

Starting to take one by one of the components in the pickers folder and convert them as it's blocking the progress of the fluent project unless this was already started by someone. @joschect this was assigned to you already, are you doing work on this issue?