Revert "Revert "Revert "Revert "Don't build GL on Metal, Vulkan, Dawn, Direct3D bots""""

Updated to use sentinel GL context even when GL backend is not built.

This reverts commit 1171d314efc7e131b039c94126d26575cfb9e70c.

Change-Id: Ia94bbe4865ddd4e898446c13886877c539f0eb0b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277976
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index c34c846..f39877f 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -9,7 +9,11 @@
 <Insert new notes here- top is most recent.>
   * SkImage::makeTextureImage() takes an optional SkBudgeted param
 
-  * 
+  * Made non-GL builds of GPU backend more robust.
+    https://review.skia.org/277456
+
+  * MoltenVK support removed. Use Metal backend instead.
+    https://review.skia.org/277612
 
 * * *