[canvaskit] Add tests/examples for using CanvasKit with Typescript.

This adds a way to test/demonstrate how an external client
using Typescript can make use of CanvasKit in a browser
(currently a JS library with Typescript bindings supplied).

See: modules/canvaskit/external_test/typescript_browser/

This also adds a way that we hope CanvasKit might be used
in a future release, that is, via ES6 modules.

See: modules/canvaskit/external_test/typescript_browser_es6/

These TS files can be built into the JS files needed by the
respective index.html files using the appropriate target
in modules/canvaskit/external_test/Makefile. Then, `make serve`
will bring up a HTTP Server that will make the folders
accessible on localhost:8000

Change-Id: Ie4ddc2588b4bdccd4a727f11b540289cf4f85795
Bug: skia:11077, skia:12539
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/468214
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
12 files changed