Add test configs for instanced rendering

Adds the following configs and enables them on select bots:

  glinst, glinst4, glinstdit4, glinst16, glinstdit16,
  esinst, esinst4, esinstdit4

Makes general changes to GrContextOptions, GrCaps, etc. to facilitate
this.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2182783004

Review-Url: https://codereview.chromium.org/2182783004
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 042332c..518383b 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -407,6 +407,10 @@
             ctxOptions = static_cast<GrContextFactory::ContextOptions>(
                 ctxOptions | GrContextFactory::kEnableNVPR_ContextOptions);
         }
+        if (gpuConfig->getUseInstanced()) {
+            ctxOptions = static_cast<GrContextFactory::ContextOptions>(
+                ctxOptions | GrContextFactory::kUseInstanced_ContextOptions);
+        }
         if (SkColorAndColorSpaceAreGammaCorrect(gpuConfig->getColorType(),
                                                 gpuConfig->getColorSpace())) {
             ctxOptions = static_cast<GrContextFactory::ContextOptions>(