Add D8 based desugar command

Skeleton D8 desugar command taking the same arguments as Desugar together with simple test which invoke it directly.

RELNOTES: None.
PiperOrigin-RevId: 306993018
diff --git a/src/BUILD b/src/BUILD
index 42fe065..f2a1bae 100644
--- a/src/BUILD
+++ b/src/BUILD
@@ -161,7 +161,7 @@
     # WARNING: Only adjust the number in `expect` if you are intentionally
     # adding or removing embedded tools. Know that the more embedded tools there
     # are in Bazel, the bigger the binary becomes and the slower Bazel starts.
-    expect = 470,
+    expect = 500,
     margin = 5,  # percentage
 )