vision/apiv1: add NewImage helpers
vision/apiv1: add NewImage helpers

This is the first step to removing the handwritten vision package.
Convenience features will be ported until vision can be removed.

Change-Id: Ie2797e39571fa7b25af556d22c1eb84bc94852c0
Reviewed-on: https://code-review.googlesource.com/12670
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go