Provide better user feedback when a View definition is invalid

[pcdavid]

This is the equivalent of #4389 but for View definitions, which have the same issue: a single, hard-to-find mistake in the definition can render the whole View invalid and prevent it to be deployed with no clue for the studio maker about what's wrong.

The implementation however will be very different and much more involved as we can not simply leverage EMF's validation of EPackages as we do for Domains.