Update target_sdk_version from SdkSpec to ApiLevel

target_sdk_version signifies device version and does not need an sdkKind to
describe it fully. Update the type and cleanup existing usages. As a
side benefit, we also get better error handling since users can no
longer enter something like `public_30` as a valid target_sdk_version in bp
files

Test: m nothing
Test: no change in ninja files (this should be a no-op)
Bug: 208456999

Change-Id: I3c19245e29184bd9e5660ad8981966f64dfa9424

java/app_test.go

@@ -3077,13 +3077,17 @@ func TestTargetSdkVersionManifestFixer(t *testing.T) {
 		},
 	}
 	for _, testCase := range testCases {
+		targetSdkVersionTemplate := ""
+		if testCase.targetSdkVersionInBp != "" {
+			targetSdkVersionTemplate = fmt.Sprintf(`target_sdk_version: "%s",`, testCase.targetSdkVersionInBp)
+		}
 		bp := fmt.Sprintf(`
 			android_app {
 				name: "foo",
 				sdk_version: "current",
-				target_sdk_version: "%v",
+				%s
 			}
-			`, testCase.targetSdkVersionInBp)
+			`, targetSdkVersionTemplate)
 		fixture := android.GroupFixturePreparers(
 			prepareForJavaTest,
 			android.FixtureModifyProductVariables(func(variables android.FixtureProductVariables) {
@@ -3161,16 +3165,20 @@ func TestDefaultAppTargetSdkVersionForUpdatableModules(t *testing.T) {
 		},
 	}
 	for _, testCase := range testCases {
+		targetSdkVersionTemplate := ""
+		if testCase.targetSdkVersionInBp != nil {
+			targetSdkVersionTemplate = fmt.Sprintf(`target_sdk_version: "%s",`, *testCase.targetSdkVersionInBp)
+		}
 		bp := fmt.Sprintf(`
 			android_app {
 				name: "foo",
 				sdk_version: "current",
 				min_sdk_version: "29",
-				target_sdk_version: "%v",
+				%s
 				updatable: %t,
 				enforce_default_target_sdk_version: %t
 			}
-			`, proptools.String(testCase.targetSdkVersionInBp), testCase.updatable, testCase.updatable) // enforce default target sdk version if app is updatable
+			`, targetSdkVersionTemplate, testCase.updatable, testCase.updatable) // enforce default target sdk version if app is updatable
 
 		fixture := android.GroupFixturePreparers(
 			PrepareForTestWithJavaDefaultModules,