Make getFlipperLib generally available, and use it to decouple opening links from Electron

Summary:
This stack reduces our direct dependency on Electron, for example by exposing our own API to open links.

Also exposing `getFlipperLib` as API from `flipper-plugin`, so that these utility methods are available outside plugin contexts as well.

Reviewed By: timur-valiev

Differential Revision: D29661689

fbshipit-source-id: 0c0523326eeb0d9d8fbe3e03c4609327bb53596b

desktop/flipper-plugin/src/plugin/FlipperLib.tsx

@@ -30,19 +30,20 @@ export interface FlipperLib {
     deeplink: unknown,
   ): void;
   writeTextToClipboard(text: string): void;
+  openLink(url: string): void;
   showNotification(pluginKey: string, notification: Notification): void;
   DetailsSidebarImplementation?(
     props: DetailSidebarProps,
   ): React.ReactElement | null;
 }
 
-let flipperLibInstance: FlipperLib | undefined;
+export let flipperLibInstance: FlipperLib | undefined;
 
 export function tryGetFlipperLibImplementation(): FlipperLib | undefined {
   return flipperLibInstance;
 }
 
-export function getFlipperLibImplementation(): FlipperLib {
+export function getFlipperLib(): FlipperLib {
   if (!flipperLibInstance) {
     throw new Error('Flipper lib not instantiated');
   }