Add support for parsing 'LOCAL_TARGET_SDK_VERSION' in androidmk

Update androidmk to enable parsing of 'LOCAL_TARGET_SDK_VERSION' from
an Android.mk and translating it to target_sdk_version in an Android.bp.

Bug: 313336240
Test: m androidmk
Test: androidmk vendor/xts/gts-tests/tests/assist/Android.mk
Change-Id: I465aba3ea7d22a9978fc370a6718a2cfc43dce36

androidmk/androidmk/android.go

@@ -106,6 +106,7 @@ func init() {
 			"LOCAL_ARM_MODE_HACK":           "instruction_set",
 			"LOCAL_SDK_VERSION":             "sdk_version",
 			"LOCAL_MIN_SDK_VERSION":         "min_sdk_version",
+			"LOCAL_TARGET_SDK_VERSION":      "target_sdk_version",
 			"LOCAL_NDK_STL_VARIANT":         "stl",
 			"LOCAL_JAR_MANIFEST":            "manifest",
 			"LOCAL_CERTIFICATE":             "certificate",

androidmk/androidmk/androidmk_test.go

@@ -1450,6 +1450,7 @@ LOCAL_PACKAGE_NAME := foo
 LOCAL_PRODUCT_MODULE := true
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
 LOCAL_SDK_VERSION := current
+LOCAL_TARGET_SDK_VERSION := target_version
 LOCAL_RRO_THEME := FooTheme
 
 include $(BUILD_RRO_PACKAGE)
@@ -1460,6 +1461,7 @@ runtime_resource_overlay {
 	product_specific: true,
 
 	sdk_version: "current",
+	target_sdk_version: "target_version",
 	theme: "FooTheme",
 
 }