Async rendering API and "pure" image fetching

[lordofthelake]

This opens the way to adding a pure Node.js bridge, that can be run on different platforms. It also improves significantly the rendering performance in image-heavy layouts, as the rendering doesn't stop on network requests (in an informal test by @macintoshhelper, the improvement can be as much as 2x).

Breaking changes

• render, renderToJSON and makeSymbol now are async methods, returning Promises (Proposal: making render() async #469)

Major changes

• Images now get fetched and displayed without any re-encoding, re-compression, or other manipulations.

Other changes

• Travis CI now runs the test suite on both Node.js 12.x and 14.x. The npm cache is temporarily disabled, because it causes issues with npm 7. It can probably be re-enabled if someone with admin access to Travis purges all the caches from their UI.

---

Many of the changes that were initially part of this PR have already been added by @mathieudutour in separate PR's.

# Breaking changes
* render and renderToJSON are completely split. render is meant to be used exclusively while embedded in Sketch. renderToJSON can be used in either scenario.
* There isn't a default export anymore. import ReactSketchapp from 'react-sketchapp' must now be rewritten as import * as ReactSketchapp from 'react-sketchapp'
* There are different entrypoints for each platform. It needs a somewhat recent version of skpm to bundle correctly, one that reads the sketch field in package.json.
* Platform.Version now returns the actual Sketch version the plugin is running in, as a string, instead of being fixed to be 1. If it's running under Node or another environment, it returns an empty string.

## Major changes
* render, renderToJSON, makeSymbol, TextStyles.registerStyle, TextStyles.create now take an optional extra parameter, a PlatformBridge. It is already initialized smartly for each platform, but can be overridden by the user. This opens the possibility for adding other bridges (addressing, for example, #465) or even running react-sketchapp in the browser (creating the appropriate bindings).

## Internal changes
* Platform-specific modules now use dynamic imports or double file extensions instead of using evals to throw webpack off the scent.
* Different implementations of the same methods are now grouped by method, instead of being split in different directories per platform.

[lordofthelake]

@mathieudutour Before I spend time debugging it, is npm run test:e2e supposed to work? I see it's commented out on .travis.yml and it's erroring out in a cryptic way for me, so before investing the time I wanted to figure out whether it's me or it was broken before.

npm run test:e2e

> react-sketchapp@3.0.5 test:e2e /Users/michelepiccirillo/Development/COMPOSITIVE/react-sketchapp
> skpm-test

Looking for the test files
 RUNS  basic
 RUNS  render-context
 RUNS  render-in-wrapped-object

Building the test plugin source
Compiling the test plugin
Running the tests
error Error while running the tests after build
Error: Command failed: "/Applications/Sketch.app/Contents/Resources/sketchtool/bin/sketchtool" run "/Users/michelepiccirillo/Development/COMPOSITIVE/react-sketchapp/node_modules/@skpm/test-runner/test-runner.sketchplugin" "plugin-tests" --without-activating

    at ChildProcess.exithandler (child_process.js:295:12)
    at ChildProcess.emit (events.js:210:5)
    at maybeClose (internal/child_process.js:1021:16)
    at Socket.<anonymous> (internal/child_process.js:430:11)
    at Socket.emit (events.js:210:5)
    at Pipe.<anonymous> (net.js:659:12) {
  killed: false,
  code: 1,
  signal: null,
  cmd: '"/Applications/Sketch.app/Contents/Resources/sketchtool/bin/sketchtool" run "/Users/michelepiccirillo/Development/COMPOSITIVE/react-sketchapp/node_modules/@skpm/test-runner/test-runner.sketchplugin" "plugin-tests" --without-activating'
}

[lordofthelake]

@mathieudutour Friendly ping :)
I would appreciate some feedback on whether the overall direction is to incorporate this change at all or not, since we have a bunch of work downstream influenced by this.

If affirmative, I will do the last round of polishing with docs & tests so that this can go in properly; otherwise, I'll just move on with a different approach for our code.

[mathieudutour]

Sorry for the delay. Yeah, happy with how it's going 👍

[macintoshhelper]

@mathieudutour Before I spend time debugging it, is npm run test:e2e supposed to work? I see it's commented out on .travis.yml and it's erroring out in a cryptic way for me, so before investing the time I wanted to figure out whether it's me or it was broken before.

npm run test:e2e

Hi @lordofthelake , just noticed this comment. I actually ran into the same issue on #516 . I'm working on fixing up the e2e tests, and adding e2e tests for all of the examples, with the view of integrating visual regression testing later on.

It appears to be a problem on Sketch's side with sketchtool, or with skpm-test. Importing the test plugin manually (open node_modules/@skpm/test-runner/, double clicking test-runner.sketchplugin and using sketch-dev-tools to see console logs works as a hacky fix for now.

Running npm run test:e2e in git checkout v3.0.0-beta3 should help figure out if this is an issue introduced by a Sketch update or not (e2e testing worked in that commit/git snapshot).

As mentioned in #346 , the plugin is required to export commonjs modules.

[macintoshhelper]

@lordofthelake Hi, btw, I found what was breaking the e2e tests. Adding this to the package.json should fix it (downgrading @skpm/test-runner to 0.3.x from 0.4.x):

{
// ...
  "dependencies": {
// ...
    "@skpm/test-runner": "^0.3.2",
  }

Ref: #516

[lordofthelake]

This has been around for a while, although 50%+ of the changes proposed here have already been incorporated. I have cleaned up the rest of the changes and resolved the merge conflicts.

There should probably be a major version bump with this, since the switch to returning Promises is not retro-compatible

[lordofthelake]

The build is red for what I suspect is a dirty npm cache (nodejs/help#2874). I would try to clean Travis' cache, but I don't have enough permissions to do so. Maybe @mathieudutour can help with this.