Add PLATFORM_DISPLAY_VERSION

Add PLATFORM_DISPLAY_VERSION to version_defaults.mk that will propagate
to the ro.build.version.release_or_preview_display property and
be shown as the Android version for preview releases by Settings.

Bug: 221950960
Test: manual
Change-Id: I697cc59f77f92aa98a8a2573662797e6d3bd2042
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 8ee21c8..f19e841 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -19,6 +19,7 @@
 #
 # Guarantees that the following are defined:
 #     PLATFORM_VERSION
+#     PLATFORM_DISPLAY_VERSION
 #     PLATFORM_SDK_VERSION
 #     PLATFORM_VERSION_CODENAME
 #     DEFAULT_APP_TARGET_SDK
@@ -54,6 +55,11 @@
 # release build.  If this is a final release build, it is simply "REL".
 PLATFORM_VERSION_CODENAME.TP1A := Tiramisu
 
+# This is the user-visible version.  In a final release build it should
+# be empty to use PLATFORM_VERSION as the user-visible version.  For
+# a preview release it can be set to a user-friendly value like `12 Preview 1`
+PLATFORM_DISPLAY_VERSION :=
+
 ifndef PLATFORM_SDK_VERSION
   # This is the canonical definition of the SDK version, which defines
   # the set of APIs and functionality available in the platform.  It