Add custom SystemModules to bootclasspath to reduce duplication

Adds a library dependency to each of the dummy system modules created
by testing.go so that any changes in the behavior were detected by
the existing tests which were then fixed.

Bug: 141359858
Test: m checkbuild
Change-Id: Id4442f4aa3931ac93049f3367b96a5b49cc075e1

java/testing.go

@@ -114,7 +114,13 @@ func GatherRequiredDepsForTest() string {
 	for _, extra := range systemModules {
 		bp += fmt.Sprintf(`
 			java_system_modules {
-				name: "%s",
+				name: "%[1]s",
+				libs: ["%[1]s-lib"],
+			}
+			java_library {
+				name: "%[1]s-lib",
+				sdk_version: "none",
+				system_modules: "none",
 			}
 		`, extra)
 	}