Add MaxAPIVersion to GrVkBackendContext.

This moves us to the correct way of handling the correct version of
Vulkan that the client wants us to use.

Bug: skia:
Change-Id: I6c7962b5d2d48ae142c6a701c30f5af3801ac99b
Reviewed-on: https://skia-review.googlesource.com/c/187382
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
6 files changed