Reland "Let client pass in full extension to GrVkBackendContext."

This reverts commit cb92b26e5ca6063bcf1a922109b8224e0b6eb4da.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "Let client pass in full extension to GrVkBackendContext."
> 
> This reverts commit 45c9dab4c3ec43cedb28d1b8c08e166fe0c2e767.
> 
> Reason for revert: fucshia uses GrVkBackendContext. Need to revert earlier changes
> 
> Original change's description:
> > Let client pass in full extension to GrVkBackendContext.
> > 
> > Bug: skia:
> > Change-Id: I772ab4ccbca0f4f7e7d429d6c421b07d97f0606f
> > Reviewed-on: https://skia-review.googlesource.com/131880
> > Reviewed-by: Jim Van Verth <jvanverth@google.com>
> > Commit-Queue: Greg Daniel <egdaniel@google.com>
> 
> TBR=egdaniel@google.com,jvanverth@google.com,bsalomon@google.com
> 
> Change-Id: I1a765ff406c83cb234c3614b804fbed677d5a382
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia:
> Reviewed-on: https://skia-review.googlesource.com/137901
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,jvanverth@google.com,bsalomon@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: skia:
Change-Id: I0af797c51dde705473e9afaccb1d4b4423e8c41e
Reviewed-on: https://skia-review.googlesource.com/138302
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
13 files changed