Can't edit Hz number in ringtone block in apps (keyboard doesn't pop up)

[microbit-lucy]

Describe the bug
When you use the ring tone (Hz) block it should be possible to tap the number (e.g. 262 in the example below) and type in a number. However, on a mobile device (whether in a browser or in the iOS or Android apps), the user can't edit that number - no keyboard pops up and cut/paste doesn't work either.

[Note, tapping a note on the keyboard does change this number, it just can't be edited manually.]

To Reproduce
Steps to reproduce the behavior:

1. Go to MakeCode on a mobile device - either in a Chrome browser or on the Android or iOS micro:bit app
2. Add the ring tone (Hz) block
3. Tap the number and try to change it - this isn't possible.

Expected behavior
Tapping the number field in the ring tone (Hz) block, should pop up the keyboard in Android and iOS and allow the user to enter a number.

Mobile only issue (please complete the following information):

• MakeCode in a browser on a mobile device
• MakeCode inside the iOS or Android apps

Additional context

This bug is a particular problem at the moment as it prevents a number of key projects (e.g. https://microbit.org/projects/make-it-code-it/conductivity-tester/) from being completed on a mobile device. One of these projects is part of the programme in a big roll out where tablets will be used so there is some urgency to get it fixed.