Use watcher addon api instead of promise to wait for generated files

[lifeart]

els-component-extraction-addon/index.js

Line 52 in 96dc0e9

await new Promise((resolve) => setTimeout(resolve, 2000));

type Watcher = (uri: string, change: FileChangeType) => any;
project.addWatcher(fn: Watcher);

we need to wait for watcher called with expected paths with some reasonable timeout (5s)

see lifeart/ember-language-server#12