Split out sdk.go from java.go

Split out SDK handling functions from java.go to sdk.go and tests
from java_test.go to sdk.go.

Test: sdk_test.go
Change-Id: I83ef48cbe5230572c1d4ecc0e89021d2f7c71b76
diff --git a/Android.bp b/Android.bp
index 29ad569..d5f052e 100644
--- a/Android.bp
+++ b/Android.bp
@@ -249,6 +249,7 @@
         "java/java_resources.go",
         "java/prebuilt_apis.go",
         "java/proto.go",
+        "java/sdk.go",
         "java/sdk_library.go",
         "java/support_libraries.go",
         "java/system_modules.go",
@@ -258,6 +259,7 @@
         "java/dexpreopt_test.go",
         "java/java_test.go",
         "java/jdeps_test.go",
+        "java/sdk_test.go",
     ],
     pluginFor: ["soong_build"],
 }