fix(ios-debugging): Close frontend socket unconditionally

[mbektchiev]

There's no need to keep the frontend socket open after its corresponding
backend socket disconnects. This misleads the Inspector UI that it
is still connected with a backend.

A part of the fix to NativeScript/ios-jsc#927

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/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.
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• Tests for the changes are included.

What is the current behavior?

When the backend socket disconnects, the frontend socket is closed only if tns debug --no-watch is used.

What is the new behavior?

When the backend socket disconnects, the frontend socket is closed unconditionally.