Export LocationsContext in @leanprover/infoview (#379)

The `LocationsContext` is exported in `infoview/goalLocation.tsx` but not in the `.index.tsx` file.

lean4-infoview/src/index.tsx

@@ -12,7 +12,7 @@ export { EditorContext, VersionContext } from './infoview/contexts';
 export { EditorConnection } from './infoview/editorConnection';
 export { RpcContext } from './infoview/rpcSessions';
 export { ServerVersion } from './infoview/serverVersion';
-export { GoalLocation, GoalsLocation } from './infoview/goalLocation';
+export { LocationsContext, GoalLocation, GoalsLocation } from './infoview/goalLocation';
 export { importWidgetModule, DynamicComponent, DynamicComponentProps,
     PanelWidgetProps } from './infoview/userWidget';