feat(fs): accept baseDir in size (#3623)

In plugins/fs/guest-js/index.ts, the size function only sent `path`
although the Rust command accepts `options.baseDir` and the JSDoc example
passed `{ baseDir: BaseDirectory.AppData }` (a TS error, silently dropped
at runtime, so the relative path was rejected).

Adds an optional `options?: SizeOptions` parameter (new exported type).
api-iife.js regenerated. The e2e spec now measures a file and a directory
relative to AppData instead of working around the missing option.

plugins/fs/guest-js/index.ts

@@ -1493,6 +1493,16 @@ async function watchImmediate(
   })
 }
 
+/**
+ * Options for the `size` function.
+ *
+ * @since 2.6.0
+ */
+interface SizeOptions {
+  /** Base directory for `path`. */
+  baseDir?: BaseDirectory
+}
+
 /**
  * Get the size of a file or directory. For files, the `stat` functions can be used as well.
  *
@@ -1507,16 +1517,21 @@ async function watchImmediate(
  * ```
  *
  * @param path The path of the file or directory to measure.
+ * @param options Options defining the base directory of `path` (since 2.6.0).
  * @returns A promise resolving to the size in bytes.
  * @since 2.1.0
  */
-async function size(path: string | URL): Promise<number> {
+async function size(
+  path: string | URL,
+  options?: SizeOptions
+): Promise<number> {
   if (path instanceof URL && path.protocol !== 'file:') {
     throw new TypeError('Must be a file URL.')
   }
 
   return await invoke('plugin:fs|size', {
-    path: path instanceof URL ? path.toString() : path
+    path: path instanceof URL ? path.toString() : path,
+    options
   })
 }
 
@@ -1609,6 +1624,7 @@ export type {
   TruncateOptions,
   WriteFileOptions,
   ExistsOptions,
+  SizeOptions,
   FileInfo,
   WatchOptions,
   DebouncedWatchOptions,