[sf] Fix layer ids for background color layers

Fixes a regression caused by Ie0f93ca956e6d043c9d95d00bc205d242e47c4cc
which created duplicate layer ids.

Also deflakes corner radius tests by tracking eCornerRadiusChanged state
changes correctly.

Test: presubmit w/new fe
Bug: 238781169

Change-Id: I2d5321b5ba77e1074ef039bcd90c78e82c1a0049
diff --git a/services/surfaceflinger/FrontEnd/LayerCreationArgs.cpp b/services/surfaceflinger/FrontEnd/LayerCreationArgs.cpp
index cfa2b03..97af445 100644
--- a/services/surfaceflinger/FrontEnd/LayerCreationArgs.cpp
+++ b/services/surfaceflinger/FrontEnd/LayerCreationArgs.cpp
@@ -50,7 +50,7 @@
     }
 
     if (internalLayer) {
-        sequence = getInternalLayerId(sInternalSequence++);
+        sequence = id.value_or(getInternalLayerId(sInternalSequence++));
     } else if (id) {
         sequence = *id;
         sSequence = *id + 1;