Console error reported for serial_redirect

Describe the bug

In a new project, the first opening of the Serial toolbox panel triggers a browser console error

I think this may be because the rate parameter description "e.g." is picked up as a default value

https://github.com/microsoft/pxt-microbit/blob/ee22e9919b81d243a7e47f9d31349846e38a27e5/libs/core/serial.cpp#L161

https://github.com/microsoft/pxt-microbit/blob/ee22e9919b81d243a7e47f9d31349846e38a27e5/libs/core/shims.d.ts#L1068

To Reproduce
Steps to reproduce the behavior:

1. Go to https://makecode.microbit.org/
2. Create a new project and open the browser console
3. Open the Serial toolbox panel
4. See error

Expected behavior
A correct default value is specified

Screenshots

micro:bit version (please complete the following information):
not hardware related

Desktop (please complete the following information):

• OS: [e.g. iOS] Windows
• Browser [e.g. chrome, safari] Chrome
• Version [e.g. 22]

Inspect libs/core/serial.cpp around line 161 and libs/core/shims.d.ts around line 1068, then reproduce the issue by opening the Serial toolbox in a new project with the browser console open. Confirm the parameter metadata produces the reported console error, and consider the work complete when a correct default value is specified and the error no longer appears.