add a new test on valid escaped from as identifier

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/input.js

@@ -0,0 +1 @@
+export default \u{66}rom;

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": ["exportDefaultFrom"],
+  "sourceType": "module"
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/output.json

@@ -0,0 +1,22 @@
+{
+  "type": "File",
+  "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+        "declaration": {
+          "type": "Identifier",
+          "start":15,"end":24,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":24},"identifierName":"from"},
+          "name": "from"
+        }
+      }
+    ],
+    "directives": []
+  }
+}