Avoid duplication of ThemeProperty type

src/sidebar/helpers/theme.js

+/**
+ * @typedef {import('../../types/config').ThemeProperty} ThemeProperty
+ */
+
+/** @type {Record<ThemeProperty, string>} */
 const supportedThemeProperties = {
   accentColor: 'color',
   appBackgroundColor: 'backgroundColor',
@@ -7,12 +12,6 @@ const supportedThemeProperties = {
   annotationFontFamily: 'fontFamily',
 };
 
-/**
- * Name of a theme element which can be configured.
- *
- * @typedef {keyof supportedThemeProperties} ThemeProperty
- */
-
 /**
  * Subset of the config from the host page which includes theme configuration.
  *