Watcher infrastructure (#1724)

* wip

* Adding chokidar and types

* specifiying build tasks

* new structure, new types, executor and watchers

* Adding log

* Fully implemented watchers

* adapt vscode launc

* Add .babelrc.js to toplevel tsconfig project

* Typo

* Get schema path from .graphqlconfig

* Use watcher binary

* Add joi validation to watcher

* Remove fb-watchman for now

* Use correct ignore path

* Fix dist folder

* Allow setting watcher

* Per default only spawn one process at a time

* Support runOnInit

* Rename RestartingExecutor to LongRunningExecutor

* Use debounce instead of throttle

* Remove console log

* Debounce command execution

* Simplify debounce

* Watcher name change

* Typos

* Rename "watcher" root level config to "backend"

scripts/watcher/types.ts

@@ -0,0 +1,50 @@
+import Joi from "joi";
+
+export interface WatchOptions {
+  ignore?: ReadonlyArray<string>;
+}
+
+export interface Watcher {
+  watch(
+    paths: ReadonlyArray<string>,
+    options?: WatchOptions
+  ): AsyncIterable<string>;
+}
+
+export interface Executor {
+  onInit?(): void;
+  onCleanup?(): void;
+  execute(filePath: string): void;
+}
+
+export interface Config {
+  rootDir?: string;
+  backend?: Watcher;
+  watchers: {
+    [key: string]: WatchConfig;
+  };
+}
+
+export interface WatchConfig {
+  paths: ReadonlyArray<string>;
+  ignore?: ReadonlyArray<string>;
+  executor: Executor;
+}
+
+export const configSchema = Joi.object({
+  rootDir: Joi.string().optional(),
+  backend: Joi.object().optional(),
+  watchers: Joi.object().pattern(
+    /.*/,
+    Joi.object({
+      paths: Joi.array()
+        .items(Joi.string())
+        .unique(),
+      ignore: Joi.array()
+        .items(Joi.string())
+        .unique()
+        .optional(),
+      executor: Joi.object(),
+    })
+  ),
+});