buildinfo_prop generates ro.build.version.known_codenames

The sysprop is now generated as the corresponding Make variable
PLATFORM_VERSION_KNOWN_CODENAMES is imported.

Bug: 236602028
Test: atest ComposHostTestCases
Change-Id: Ife7e87ce5de65b57c51d5565e288807cf8360b28
diff --git a/android/variable.go b/android/variable.go
index 9478c0c..734ed1b 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -200,6 +200,7 @@
 	Platform_min_supported_target_sdk_version *string  `json:",omitempty"`
 	Platform_base_os                          *string  `json:",omitempty"`
 	Platform_version_last_stable              *string  `json:",omitempty"`
+	Platform_version_known_codenames          *string  `json:",omitempty"`
 
 	DeviceName                            *string  `json:",omitempty"`
 	DeviceProduct                         *string  `json:",omitempty"`