Add new theme for Fluent 9

[heath-freenome]

Fluent UI v9 is a separate package @fluentui/react-components that requires its own theme. We can @deprecate the current fluent-ui theme and build a new one called fluentui-rc (or a better name), by copying the current theme and making the necessary changes

[marcveens]

I'd like to help with this one. Do you know if anyone else already made a start?

[heath-freenome]

@marcveens You are most welcome to do the work for this! If you have any questions you can either ask directly or show up for the Friday meetings listed in this issue