Increase GrMtlPipelineState caches size by 8x

Users with the Finch trial enabled are seeing slow tab switches due
to MTLRenderPipelineStates being rebuilt.

Bug: chromium:974219 chromium: 988964
Change-Id: I83adf06b7174e9f11a38da421f66a3921d17dbcf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235878
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Christopher Cameron <ccameron@chromium.org>

src/gpu/mtl/GrMtlResourceProvider.h

@@ -65,7 +65,7 @@ private:
         enum {
             // We may actually have kMaxEntries+1 PipelineStates in context because we create a new
             // PipelineState before evicting from the cache.
-            kMaxEntries = 128,
+            kMaxEntries = 1024,
         };
 
         struct Entry;