Require stencil bits on wrapped GrBackendRenderTargets to 0, 8, or 16.

This will allow us in a follow on change to put in a "fake" gl stencil
format for the wrapped FBO.

Bug: skia:10727
Change-Id: Iba1eca5114b34d25e6a220591d28a20f7b36b12b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321545
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index 7c728d9..50aba4e 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -9,6 +9,10 @@
 
   * <insert new release notes here>
 
+  * GrBackendRenderTargets which are created with a stencilBits param, now require
+    the stencilBits to be 0, 8, or 16.
+    https://review.skia.org/321545
+
 * * *
 
 Milestone 87