Add buildinfo_prop module

buildinfo_prop module is a replacement for build/make/tools/buildinfo.sh
so other images like microdroid can refer to build.prop.

For now, buildinfo_prop only supports a few build.prop properties, and
it's only used in microdroid.

Bug: 189164487
Test: build
Change-Id: I120654ca23a68de414df8da2051c6677afbab441
diff --git a/android/config.go b/android/config.go
index 9f1fd6a..250c312 100644
--- a/android/config.go
+++ b/android/config.go
@@ -777,6 +777,10 @@
 	return String(c.productVariables.Platform_base_os)
 }
 
+func (c *config) PlatformVersionLastStable() string {
+	return String(c.productVariables.Platform_version_last_stable)
+}
+
 func (c *config) MinSupportedSdkVersion() ApiLevel {
 	return uncheckedFinalApiLevel(19)
 }