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

engines/sample-lang/constants.ts

@@ -0,0 +1,10 @@
+/** Type for state passed to renderer */
+export type RS = { value: number };
+
+/** Sample program */
+export const sampleProgram = [
+  "ADD 10",
+  "SUBTRACT 4",
+  "MULTIPLY 3",
+  "DIVIDE 2",
+].join("\n");