build(docs-infra): change build-with-ivy script to switch-to-ivy (#29989)

Previously, the `build-with-ivy` script could be used to build the `aio`
project with Ivy (once it had been prepared with `ivy-ngcc`, etc.) and
then restored the configuration (e.g. `tsconfig.json`) to non-ivy mode.

As a result, it was not useful for running other commands (e.g. unit/e2e
tests) in Ivy mode.

This commit renames the script to `switch-to-ivy` and employs a
different model (similar to `ng-packages-installer`), where the project
is setup to run in Ivy mode and then all subsequent commands are
executed in that mode (until restored).

Since this is currently only used on CI, there is no automatic way to
switch back to non-ivy mode (but it could be implemented in the future
if needed).

Finally, the script now modifies `src/tsconfig.app/json` instead of
`tsconfig.json` to ensure that the `angularCompilerOptions` are not
ignored/overwritten. This is also closer to what the cli generates
with the `--enable-ivy` option.

PR Close #29989

aio/scripts/switch-to-ivy.js

@@ -0,0 +1,45 @@
+#!/usr/bin/env node
+
+// Imports
+const {extend, parse} = require('cjson');
+const {readFileSync, writeFileSync} = require('fs');
+const {join, resolve} = require('path');
+const {exec, set} = require('shelljs');
+
+set('-e');
+
+// Constants
+const ROOT_DIR = resolve(__dirname, '..');
+const TS_CONFIG_PATH = join(ROOT_DIR, 'src/tsconfig.app.json');
+const NG_COMPILER_OPTS = {
+  angularCompilerOptions: {
+    // Related Jira issue: FW-737
+    allowEmptyCodegenFiles: true,
+    enableIvy: true,
+  },
+};
+
+// Run
+_main(process.argv.slice(2));
+
+// Functions - Definitions
+function _main() {
+  // Enable Ivy in TS config.
+  console.log(`\nModifying \`${TS_CONFIG_PATH}\`...`);
+  const oldTsConfigStr = readFileSync(TS_CONFIG_PATH, 'utf8');
+  const oldTsConfigObj = parse(oldTsConfigStr);
+  const newTsConfigObj = extend(true, oldTsConfigObj, NG_COMPILER_OPTS);
+  const newTsConfigStr = JSON.stringify(newTsConfigObj, null, 2);
+  console.log(`\nNew config: ${newTsConfigStr}`);
+  writeFileSync(TS_CONFIG_PATH, newTsConfigStr);
+
+  // Run ngcc.
+  const ngccArgs = '--loglevel debug --properties es2015 module';
+  console.log(`\nRunning ngcc (with args: ${ngccArgs})...`);
+  exec(`yarn ivy-ngcc ${ngccArgs}`);
+
+  // Done.
+  console.log('\nReady to build with Ivy!');
+  console.log('(To switch back to ViewEngine (with packages from npm), undo the changes in ' +
+              `\`${TS_CONFIG_PATH}\` and run \`yarn aio-use-npm && yarn example-use-npm\`.)`);
+}