extension: import js-green-licenses for license checking

github.com/google/js-green-licenses is the license checker
used by many google-authored open source JS/TS projects.
Use it instead of using ./extension/tools/license.sh

Usage:
 cd extension; npx jsgl --local .

Configured js-green-licenses to skip checking on the
es5class package. This package was published long ago
and the last version lacks the license metadata
so js-green-licenses cannot process it.
A new version to fix the metadata won't be published
since it is officially deprecated (for a while).
The latest version was published with MIT license
(https://github.com/pocesar/ES5-Class/blob/master/LICENSE)

Change-Id: I952938cbc56aa93258de43653d531e405ea40683
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/610257
Commit-Queue: Hyang-Ah Hana Kim <hyangah@gmail.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>

Author: hyangah

extension/js-green-licenses.json

@@ -0,0 +1,5 @@
+{
+  "packageAllowlist": [
+    "es5class"
+  ]
+}