Add $mock.intersection to Mock module

[pierroberto]

$mock module supports only unions of mocks ($mock.union).

It could be useful to have intersections of mocks as follows:

const mockA = $mock.struct({ a: $mock.string })
const mockB = $mock.struct({ b: $mock.number })

const mockC = $mock.intersection(mockA, mockB)

Something similar, currently can be achieved this way:

const mockC = pipe(
  mockA,
  $mock.bindTo('mockA'),
  $mock.apS('mockB', mockB),
  $mock.map(({ mockA, mockB }) => ({
    ...mockA,
    ...mockB,
  }))
)