Move vendor snapshot tests into vendor_snapshot_test.go

Move the vendor snapshot tests into vendor_snapshot_test.go to
reduce the size of cc_test.go

Bug: 177098205
Test: go test ./build/soong/cc/...
Change-Id: Ib1120f986fc0111a9487fce00539a4c5ae7e2e87
diff --git a/cc/Android.bp b/cc/Android.bp
index 33f3db2..6ec7e0e 100644
--- a/cc/Android.bp
+++ b/cc/Android.bp
@@ -87,6 +87,7 @@
         "prebuilt_test.go",
         "proto_test.go",
         "test_data_test.go",
+        "vendor_snapshot_test.go",
     ],
     pluginFor: ["soong_build"],
 }