Implement basic execution system and UI

This is a rather large commit that includes all of the following:
- React UI with code editor, runtime renderer and input-output panes
- Language providers for a sample language and Brainfuck
- Implementation of code execution in a web worker
- All-at-once unabortable execution of program fully functional

ui/MainLayout.tsx

@@ -0,0 +1,58 @@
+import React from "react";
+import { Mosaic, MosaicNode, MosaicWindow } from "react-mosaic-component";
+
+// IDs of windows in the mosaic layout
+type WINDOW_ID = "editor" | "renderer" | "input" | "output";
+
+const WindowTitles = {
+  editor: "Code Editor",
+  renderer: "Visualization",
+  input: "User Input",
+  output: "Execution Output",
+};
+
+type Props = {
+  renderEditor: () => React.ReactNode;
+  renderRenderer: () => React.ReactNode;
+  renderInput: () => React.ReactNode;
+  renderOutput: () => React.ReactNode;
+};
+
+export const MainLayout = (props: Props) => {
+  const MOSAIC_MAP = {
+    editor: props.renderEditor,
+    renderer: props.renderRenderer,
+    input: props.renderInput,
+    output: props.renderOutput,
+  };
+
+  const INITIAL_LAYOUT: MosaicNode<WINDOW_ID> = {
+    direction: "row",
+    first: "editor",
+    second: {
+      direction: "column",
+      first: "renderer",
+      second: {
+        direction: "row",
+        first: "input",
+        second: "output",
+      },
+    },
+  };
+
+  return (
+    <Mosaic<keyof typeof MOSAIC_MAP>
+      className="mosaic-blueprint-theme bp3-dark"
+      initialValue={INITIAL_LAYOUT}
+      renderTile={(windowId, path) => (
+        <MosaicWindow<number>
+          path={path}
+          title={WindowTitles[windowId]}
+          toolbarControls={<span />}
+        >
+          {MOSAIC_MAP[windowId]()}
+        </MosaicWindow>
+      )}
+    />
+  );
+};