Proposal: `ng doctor` for check diff and sync to the latest project template

### Bug Report or Feature Request (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```

### Desired functionality.
After updated the CLI version, sometimes `package.json` is updated. Currently `package.json` is generated at `ng new` and never do sync to latest dependencies.

I want something like `ng doctor` to solve it. The use-case images are below:

```
$ ng doctor # listing up dependency changes
$ ng doctor --write # auto-patching on _compatible_ version (with semver ?)
```

### Mention any other details that might be useful.

Start with the proposed `ng doctor` entry point and the existing `package.json` generation path. Define how dependency differences are listed and how `--write` applies only semver-compatible updates, then add coverage for both listing changes and writing updates.

Written by the indexing model from the issue text.