Exporting MakeBazelTarget() in testing.go

Since we are putting conversion tests in the same
package as the module being converted from now on

Test: m bp2build
Change-Id: Ied53589d497fef70bfa11d8f6067459c9a50cd72
diff --git a/bp2build/java_import_conversion_test.go b/bp2build/java_import_conversion_test.go
index 707ecce..05d7142 100644
--- a/bp2build/java_import_conversion_test.go
+++ b/bp2build/java_import_conversion_test.go
@@ -45,7 +45,7 @@
 }
 `,
 		ExpectedBazelTargets: []string{
-			makeBazelTarget("java_import", "example_import", AttrNameToString{
+			MakeBazelTarget("java_import", "example_import", AttrNameToString{
 				"jars": `["import.jar"]`,
 			}),
 		}})
@@ -74,7 +74,7 @@
 }
 `,
 		ExpectedBazelTargets: []string{
-			makeBazelTarget("java_import", "example_import", AttrNameToString{
+			MakeBazelTarget("java_import", "example_import", AttrNameToString{
 				"jars": `select({
         "//build/bazel/platforms/os:android": ["android.jar"],
         "//build/bazel/platforms/os:linux": ["linux.jar"],