Add context option to webpack config

For achieving deterministic builds

packages/ember-auto-import/ts/webpack.ts

@@ -129,6 +129,16 @@ export default class WebpackBundler extends Plugin implements Bundler {
     let config: Configuration = {
       mode: this.opts.environment === 'production' ? 'production' : 'development',
       entry,
+      // Pursuant to the webpack docs (https://webpack.js.org/configuration/entry-context/#context),
+      // we follow the recommendation to set the context, i.e. the absolute path for resolving 
+      // entry points and loaders from the configuration. By doing this, the config becomes
+      // independent of the current working directory, and importantly ensures that we get DETERMINISTIC
+      // builds (i.e. produced assets have invariant content across repeated identical builds).
+      // If we didn't do this, the module names that webpack considers for computing the deterministic 
+      // "moduleIds" (using the default moduleIds: "deterministic" option) would end up being
+      // based on broccoli temp-directory paths, which aren't deterministic across builds, and would
+      // hence cause output assets to also be non-deterministic.
+      context: stagingDir,
       performance: {
         hints: false,
       },