Port phoneNum validator to the develop

[Fifciu]

Todo

• Close this one: Bug/phone num vsf-default#62
• Remove phoneNum from 1.12.3: https://github.com/vuestorefront/vue-storefront/blob/hotfix/v1.12.3/core/helpers/validators/index.ts
• Add phoneNum to the develop: https://github.com/vuestorefront/vue-storefront/blob/develop/core/helpers/validators/index.ts
• Add unit tests for phoneNum to the develop

Version of Vue Storefront

• Vue Storefront
• Vue Storefront Next

Can you handle fixing this bug by yourself?

• YES
• NO

Which Release Cycle state this refers to? Info for developer. (doesn't apply to Next)

Pick one option.

• This is a bug report for test version on https://test.storefrontcloud.io - In this case Developer should create branch from develop branch and create Pull Request 2. Feature / Improvement back to develop.
• This is a bug report for current Release Candidate version on https://next.storefrontcloud.io - In this case Developer should create branch from release branch and create Pull Request 3. Stabilisation fix back to release.
• This is a bug report for current Stable version on https://demo.storefrontcloud.io and should be placed in next stable version hotfix - In this case Developer should create branch from hotfix or master branch and create Pull Request 4. Hotfix back to hotfix.

[lukaszjedrasik]

• Removed phoneNum from 1.12.3: Removed phoneNum #5736
• Added phoneNum to the develop + unit tests: Added phone num #5737