Introduce BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES

If BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES has a numeric value,
it replaces "current" or "system_current" with the version which
the flag indicates.

Bug: 163009188
Test: BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES=29 m, and then check if every vendor
java module's sdk_version is 29 if its sdk_version was current.

Change-Id: I17b49b8e02caf2d1bc57b91648d4420f3ad9fcb9
diff --git a/android/variable.go b/android/variable.go
index 1f21f34..53f081e 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -166,13 +166,14 @@
 	Platform_min_supported_target_sdk_version *string  `json:",omitempty"`
 	Platform_base_os                          *string  `json:",omitempty"`
 
-	DeviceName              *string  `json:",omitempty"`
-	DeviceArch              *string  `json:",omitempty"`
-	DeviceArchVariant       *string  `json:",omitempty"`
-	DeviceCpuVariant        *string  `json:",omitempty"`
-	DeviceAbi               []string `json:",omitempty"`
-	DeviceVndkVersion       *string  `json:",omitempty"`
-	DeviceSystemSdkVersions []string `json:",omitempty"`
+	DeviceName                            *string  `json:",omitempty"`
+	DeviceArch                            *string  `json:",omitempty"`
+	DeviceArchVariant                     *string  `json:",omitempty"`
+	DeviceCpuVariant                      *string  `json:",omitempty"`
+	DeviceAbi                             []string `json:",omitempty"`
+	DeviceVndkVersion                     *string  `json:",omitempty"`
+	DeviceCurrentApiLevelForVendorModules *string  `json:",omitempty"`
+	DeviceSystemSdkVersions               []string `json:",omitempty"`
 
 	DeviceSecondaryArch        *string  `json:",omitempty"`
 	DeviceSecondaryArchVariant *string  `json:",omitempty"`