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

android/variable.go

@@ -199,6 +199,7 @@ type productVariables struct {
 	Platform_preview_sdk_version              *string  `json:",omitempty"`
 	Platform_min_supported_target_sdk_version *string  `json:",omitempty"`
 	Platform_base_os                          *string  `json:",omitempty"`
+	Platform_version_last_stable              *string  `json:",omitempty"`
 
 	DeviceName                            *string  `json:",omitempty"`
 	DeviceProduct                         *string  `json:",omitempty"`