feat: expose getCurrentInstance like in Vue 3

Author: Guillaume Chau

src/index.ts

@@ -24,6 +24,9 @@ export default plugin;
 export { default as createElement } from './createElement';
 export { SetupContext };
 export { createComponent, ComponentRenderProxy, PropType, PropOptions } from './component';
+// For getting a gold of the interal instance in setup() - useful for advanced
+// plugins
+export { getCurrentVM as getCurrentInstance } from './runtimeContext';
 
 export * from './apis/state';
 export * from './apis/lifecycle';