String import/export specifier (#12091)

* feat: parse moduleExportName
* feat: add validators
* Support string specifier name in commonjs transform
* Support string specifier name in export-ns-from
* test: add loose testcases
* test: add testcases for amd and umd
* feat: support systemjs
* test: update fixtures fixed in #12110
* add plugin name typings
* test: rename test layout
* feat: implement under moduleStringNames flag
* chore: add plugin syntax module string names
* feat: support ModuleExportName as ModuleExportName
* test: update test fixtures
* fix flow errors
* docs: update AST spec
* feat: support { "some imports" as "some exports" }
* feat: support { "some imports" as "some exports" } in systemjs
* test: add test on `import { "foo" }`
* Address review comments
* add moduleStringNames to missing plugin helpers
* Apply suggestions from code review
* update test fixtures
* Update packages/babel-parser/src/parser/error-message.js
* update test fixtures

Co-Authored-By: Kai Cataldo <kai@kaicataldo.com>
Co-authored-by: Brian Ng <bng412@gmail.com>

packages/babel-plugin-transform-modules-systemjs/package.json

@@ -16,6 +16,7 @@
     "@babel/helper-hoist-variables": "workspace:^7.10.4",
     "@babel/helper-module-transforms": "workspace:^7.10.5",
     "@babel/helper-plugin-utils": "workspace:^7.10.4",
+    "@babel/helper-validator-identifier": "workspace:^7.10.4",
     "babel-plugin-dynamic-import-node": "^2.3.3"
   },
   "keywords": [