refactor(dev-infra): use the exec() helper from utils/shelljs whenever possible (#37444)

There is an `exec()` helper provided by `utils/shelljs.ts`, which is a
wrapper around ShellJS' `exec()` with some default options (currently
`silent: true`). The intention is to avoid having to pass these options
to every invocation of the `exec()` function.

This commit updates all code inside `dev-infra/` to use this helper
whenever possible).

NOTE: For simplicity, the `utils/shelljs` helper does not support some
      of the less common call signatures of the original `exec()`
      helper, so in some cases we still need to use the original.

PR Close #37444

dev-infra/utils/shelljs.ts

@@ -6,9 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {exec as _exec, ShellString} from 'shelljs';
+import {exec as _exec, ExecOptions, ShellString} from 'shelljs';
 
 /* Run an exec command as silent. */
-export function exec(cmd: string): ShellString {
-  return _exec(cmd, {silent: true});
+export function exec(cmd: string, opts?: ExecOptions&{async?: false}): ShellString {
+  return _exec(cmd, {silent: true, ...opts});
 }