[extensions] Setup `typescript` package with not `devDependencies` but `dependencies`

When we start to develop extensions with `ext:dev:init`, auto created `pacakges.json` has `typescript` dependency in `devDependencies`.
https://github.com/firebase/firebase-tools/blob/c0a59a59ca9230a98713553a1c0335d6957be154/templates/extensions/typescript/package.lint.json#L24

However, during `ext:dev:upload` the `npm clean-install` is run with the `--production` flag, which causes "devDependencies" to be ignored. If the package is placed in `devDependencies`, the below error occurs.
```sh
Error: generic::invalid_argument: failed to build ExtensionVersion "EXTENSION_NAME" source: failed to build NPM package:
```

So, we have to replace `typescript` package from `devDependencies` to `dependencies` whenever developing new extension.

**Expected**

The `typescript` package should be placed with `dependencies` during setup to prevent developer confusion. But, it is just my idea, could you let me know if there are any reasons why it should be placed in devDependencies.

Thanks.