ci(docs-infra): store JS bundles as CI artifacts to debug size check flakes (#37703)

As reported in #37699, the size of the main angular.io bundle sometimes
ends up bigger than expected on CI. This usually goes away after
rerunning the job a couple of times.

It is unclear what is causing this. In order to help debug the issue,
this commit stores the JS files that are checked as part of the aio
payload-size check as CI artifacts, where they can be retrieved from and
inspected.

PR Close #37703

aio/scripts/prepare-size-debug-artifacts.js

@@ -0,0 +1,24 @@
+#!/usr/bin/env node
+const {cp, ls, mkdir, set} = require('shelljs');
+const {join, resolve} = require('path');
+set('-e');
+
+// Read input arguments.
+const [sizesTarget, artifactsRelativeDir] = process.argv.slice(2);
+
+// Compute paths.
+const projectDir = resolve(__dirname, '../..');
+const sizesFilePath = join(projectDir, 'goldens/size-tracking/aio-payloads.json');
+const distDir = join(projectDir, 'aio/dist');
+const artifactsDir = resolve(projectDir, artifactsRelativeDir);
+
+// Determine which files need to be copied.
+const fileNamePrefixes = Object.keys(require(sizesFilePath)[sizesTarget].master.uncompressed);
+const filesToCopyRe = new RegExp(`^(?:${fileNamePrefixes.join('|')})\\..+\\.js$`);
+const filesToCopy = ls(distDir)
+    .filter(file => filesToCopyRe.test(file))
+    .map(file => join(distDir, file));
+
+// Copy files to the specified directory.
+mkdir('-p', artifactsDir);
+cp(filesToCopy, artifactsDir);