Rename optimizer buck target to be more specific (#4509)

Summary:
Pull Request resolved: #4509

We might add more later so start with specifying the name

Reviewed By: lucylq

Differential Revision: D60611366

fbshipit-source-id: 730d7b8be5b544e6ed4a8ad7a2aa7bb7b71ce45f

Author: JacobSzwejbka

extension/training/optimizer/targets.bzl

@@ -26,7 +26,7 @@ def define_common_targets():
             ]
 
         runtime.cxx_library(
-            name = "optimizer" + aten_suffix,
+            name = "sgd" + aten_suffix,
             srcs = [
                 "sgd.cpp",
             ],

extension/training/optimizer/test/targets.bzl

@@ -15,7 +15,7 @@ def define_common_targets():
                 "sgd_test.cpp",
             ],
             deps = [
-                "//executorch/extension/training/optimizer:optimizer" + aten_suffix,
+                "//executorch/extension/training/optimizer:sgd" + aten_suffix,
                 "//executorch/runtime/core:core",
                 "//executorch/runtime/core/exec_aten/testing_util:tensor_util",
             ],