Roll engine to 6473f1b106485cb0b4ea569af383173daeef8895 (#16032)

Includes:
* Use newer Skia API for constructing mask blur filters (flutter/engine#4875)
* Retry fixing vulkan include (flutter/engine#4874)
diff --git a/bin/internal/engine.version b/bin/internal/engine.version
index 5bf8936..037708c 100644
--- a/bin/internal/engine.version
+++ b/bin/internal/engine.version
@@ -1 +1 @@
-dd6f46c485192f4506035088c9065b9f5dbba9ab
+6473f1b106485cb0b4ea569af383173daeef8895