Add file.filesizes to recipe engine core modules.

recipe_modules/file/examples/copytree.expected/basic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[recipe_engine::file]/resources/fileutil.py",
       "--json-output",
       "/path/to/tmp/json",
       "ensure-directory",
       "--mode",
@@ skipping 83 matching lines @@
       "copy",
       "cc",
       "[START_DIR]/some dir/cc"
     ],
     "infra_step": true,
     "name": "write cc"
   },
   {
     "cmd": [
       "python",
+      "-u",
+      "RECIPE_MODULE[recipe_engine::file]/resources/fileutil.py",
+      "--json-output",
+      "/path/to/tmp/json",
+      "filesizes",
+      "a",
+      "aa",
+      "b",
+      "bb",
+      "c",
+      "cc"
+    ],
+    "infra_step": true,
+    "name": "check filesizes",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_LOG_END@filesizes@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
       "-u",
       "RECIPE_MODULE[recipe_engine::file]/resources/fileutil.py",
       "--json-output",
       "/path/to/tmp/json",
       "rmtree",
       "[START_DIR]/some other dir"
     ],
     "infra_step": true,
     "name": "make sure dest is gone"
   },
@@ skipping 160 matching lines @@
     ],
     "infra_step": true,
     "name": "remove \"some other dir/*\""
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]