Introduce types for Sandy plugins through code base

Summary:
So far there were 2 types of plugins: `FlipperPlugin` and `FlipperDevicePlugin`. This introduces a third kind: `SandyPluginDefinition`.

Unlike with the old plugins, the export of the module is not directly exposed as the plugin definition. Rather, we use class `SandyPluginDefinition` (instance) that holds a loaded definition and its meta data separately (`PluginDetails`). This means that we don't have to mix in and mutate loaded definitions, and that for unit tests we can avoid needing to provide a bunch of meta data. This also prevents a bunch of meta data existing on two places: on the loaded classes as static fields, and in the meta data field of the loaded class as well. Finally, we can now freely extends the `PluginDetails` interface in flipper, without needing to store it on the loaded classes and we are sure that no naming conflicts are caused by this in the future.

For compatibility with the existing code base, common fields are delegated from the `SandyPluginDefinition` class to the meta data.

Also cleaned up types around plugins a little bit and removed some unnecessary casts.

For all features that reason about plugins in general (such as exports), sandy plugins are ignored for now.

`SandyPluginInstance` is worked out in further diffs

The `instanceof` calls are replaced by a utility function in later diffs.

{F241363645}

Reviewed By: jknoxville

Differential Revision: D22091432

fbshipit-source-id: 3aa6b12fda5925268913779f3c3c9e84494438f8

desktop/.eslintrc.js

@@ -15,6 +15,7 @@ const pattern = /^\*\r?\n[\S\s]*Facebook[\S\s]* \* @format\r?\n/;
 const builtInModules = [
   'flipper',
   'flipper-plugin',
+  'flipper-plugin-lib',
   'react',
   'react-dom',
   'electron',