feat(ios): 'ns widget ios' for single command widget generator

[NathanWalker]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

iOS Widget/Extensions currently require a lot of manual setup to integrate.

What is the new behavior?

Introduces ns widget ios with prompts for a single command generator which even sets up a local shared Swift package to share Widget model/attributes between the host app and the widget (to not have to duplicate swift files). It also auto-updates config's to support them.

#4472
#5520
#5291