Flattens all components in a Figma file. Note that this script assumes that (1) every component in the file is an icon, (2) each icon contains a single color, and (3) the icons don't use masks. The `figma.flatten` function may not work as you expect if one of these conditions aren't met.

flatten-icons.ts

// Create a list of all component nodes in the Figma file.
const componentNodes = figma.root.children.flatMap(pageNode => {
  return pageNode.findAll(node => node.type === 'COMPONENT');
}) as readonly ComponentNode[];

// Create a list of component nodes that have more than one child node.
const unflattenedComponentNodes = componentNodes.filter(componentNode => {
  const childrenNodes = componentNode.findAll(() => true);
  return childrenNodes.length > 1;
});

// Flatten each component node's children into a single node.
unflattenedComponentNodes.forEach(node => figma.flatten(node.children, node));

figma.notify(`✅ Flattened ${unflattenedComponentNodes.length} icon(s)`);