PlayCanvas + Standalone Viewer

[MarcusLongmuir]

Resolves #170, resolves #207, resolves #192

This PR is a significant overhaul of the frontend packages with the overall goals of:

• Adding an implementation of MML on web using PlayCanvas
• Adding a standalone viewer that will be accessible at https://viewer.mml.io/

The major change is that there is now an indirection between the implementation of the attribute handling of MML elements (e.g. m-cube) and the particular rendering/graphics engine (e.g. ThreeJS).

This results in new packages that separate the concerns.

• @mml-io/mml-web contains the networking and attribute handling
• @mml-io/mml-web-threejs contains the per-element implementations of graphics for ThreeJS
• @mml-io/mml-web-threejs-standalone contains an implementation of a standalone ThreeJS app that renders MML.

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What kind of changes does your PR introduce? (check at least one)

• Feature
• Refactor

Does your PR introduce a breaking change? (check one)

• Yes

If yes, please describe its impact and migration path for existing applications:

Any users of the mml-web package should now depend on the @mml-io/mml-web package and @mml-io/mml-web-three-standalone.

The MMLScene now takes an element as a constructor argument and requires initialising with a graphics adapter:

-  import { MMLScene } from "mml-web";
+  import { MMLScene } from "@mml-io/mml-web";
+  import {
+    StandaloneThreeJSAdapter,
+    StandaloneThreeJSAdapterControlsType,
+  } from "@mml-io/mml-web-threejs-standalone";

-  const mmlScene = new MMLScene();
+  const sceneElement = document.createElement("div");
+  sceneElement.style.width = "100%";
+  sceneElement.style.height = "100%";
+  const mmlScene = new MMLScene(sceneElement);

+  StandaloneThreeJSAdapter.create(sceneElement, {
+    controlsType: StandaloneThreeJSAdapterControlsType.DragFly,
+  }).then((graphicsAdapter) => {
+    mmlScene.init(graphicsAdapter);
+  });

Does your PR fulfill the following requirements?

• All tests are passing
• The title references the corresponding issue # (if relevant)

[github-actions]

🪓 PR closed, deleted preview at https://github.com/mml-io/mml/tree/gh-pages/pull/205/