Add support for executor definitions that point to another executor. The upcoming Angular 18 uses this feature: https://github.com/angular/angular-cli/blob/main/packages/angular_devkit/build_angular/builders.json#L4, so we need to be able to resolve the builders correctly using such a configuration. Note: the change is also in [the Angular 18 PR](https://github.com/nrwl/nx/pull/22509), where it's tested with the Angular version that requires it. I'm extracting the change to this PR to facilitate reviews and reduce the size of the Angular 18 PR. <!-- Please make sure you have read the submission guidelines before posting an PR --> <!-- https://github.com/nrwl/nx/blob/master/CONTRIBUTING.md#-submitting-a-pr --> <!-- Please make sure that your commit message follows our format --> <!-- Example: `fix(nx): must begin with lowercase` --> ## Current Behavior <!-- This is the behavior we have today --> ## Expected Behavior <!-- This is the behavior we should expect with the changes in this PR --> ## Related Issue(s) <!-- Please link the issue being fixed so it gets closed when this is merged. --> Fixes #