Since our consumer TS min bar is 3.9 for @fluentui/react version 8, but our repo is compiling with TS 4.1, we need to ensure we don't introduce any TS 3.9-incompatible public APIs or .d.ts.

A "good enough" approach (may not catch all cases but is easy to implement):

• In a temp directory, scaffold a basic package with TS 3.9 and relevant fluentui deps (gzipped local versions, similar to projects-test)
• Make an index file with does export * from /*all the fluentui deps*/ -- basically just something to get TS to parse all the .d.ts files for exported stuff
• Attempt to compile

OPEN QUESTION: what's the consumer TS minbar for converged? Does it need to be included in this test?