Adding TS plugins outside of working directory

[geelen]

Following on from #306, and fab-spec/plugin-add-fab-id#2, I've discovered that the @rollup/plugin-typescript is failing to activate on paths outside of the root directory of the project. Weirdly, when running yarn link @fab/actions to test things locally, it doesn't fail, nor can I reproduce the exact failure in #306 itself.

Basically, something strange in the neighbourhood.

In investigating, I've found that @rollup/plugin-typescript has moved on several versions and now does real typechecking, whereas we are using an old version that just strips the types and calling tsc in a separate thread. So I think the best solution would be to move to @rollup/plugin-sucrase which has the type-annotation-stripping behaviour we want.

TL;DR TODO: switch to sucrase in the rollup