Validate which directives can co-exist

[CNAChino]

Is your feature request related to a problem? Please describe.

No, just an enhancement on validation

Describe the solution you'd like

I'm thinking this should be done on pre-merge. A map of directives it is not allowed to co exist. Example:

@resolver -> @external, @requires, @provides, ...

[ashpak-shaikh]

Whenever there is the following pair of directives that exist together, throw error

resolver and external
resolver and provides
resolver and requires
resolver and provides

[vijayakinbox]

Hi Ashpak, I will work on this issue. Please assign it to me.