fix: fix definition files so nativescript-cloud can be successfully built

[Fatme]

Currently nativescript-cloud cannot be built with latest master branch of CLI due to the following errors:

node_modules/nativescript/lib/definitions/project.d.ts(476,96): error TS2503: Cannot find namespace 'IXcode'.
node_modules/nativescript/lib/definitions/project.d.ts(476,165): error TS2503: Cannot find namespace 'IXcode'.
node_modules/nativescript/lib/definitions/project.d.ts(479,128): error TS2503: Cannot find namespace 'IXcode'.
node_modules/nativescript/lib/definitions/project.d.ts(480,99): error TS2503: Cannot find namespace 'IXcode'.

The issue happens as IXcode interface is already used from project.d.ts file. As nativescript-cloud lib generates references.d.ts file with references to all .d.ts files from NativeScript CLI, we need a separate .d.ts file for IXcode interface. This way, it will be included in the generated references.d.ts file and cloud-lib will be successfully built.

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.
• 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?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].