wasm: sanitize title contents

[mcginty]

If users of the crate set titles with any kind of untrusted input like a tag, filename, or whatever, arbitrary HTML can be inserted.

Reproduction

Modify https://github.com/PolyMeilex/rfd/blob/master/examples/web-trunk/src/main.rs#L17 to contain:

-        let task = rfd::AsyncFileDialog::new().pick_file();
+        let task = rfd::AsyncFileDialog::new()
+            .set_title(r#"<img src=x onerror="alert('HACK THE PLANET')">"#)
+            .pick_file();

then run trunk serve and click the rfd button.