Fix: specify @default undefined for undefined prop values

[metonym]

Currently, exported props that are undefined by default do not have a corresponding @default comment in the generated TypeScript definition.

Input

<script>
  /** @type {boolean} */
  export let prop;
</script>

Current output

export interface InputProps {
  prop?: boolean;
}

Expected output

export interface InputProps {
+  /**
+   * @default undefined
+   */
  prop?: boolean;
}

Fixes

• specify @default undefined for undefined prop values in TypeScript definitions
• use <code>undefined</code> instead of -- for undefined default values in Markdown