src/vs/editor/browser/config/migrateOptions.ts/EditorSettingMigration/_write
class EditorSettingMigration:	private static _write(target: any, key: string, value: any): void {
		const firstDotIndex = key.indexOf('.');
		if (firstDotIndex >= 0) {
			const firstSegment = key.substring(0, firstDotIndex);
			target[firstSegment] = target[firstSegment] || {};
			this._write(target[firstSegment], key.substring(firstDotIndex + 1), value);
			return;
		}
		target[key] = value;
	}