Using a monitor to change a variable/list does not trigger project changed

[kchadha]

Expected Behavior

Changing the value of a variable through a monitor (e.g. adding/deleting items from list monitors, changing value of scalar var using slider) should trigger "save now".

Actual Behavior

Related to #2021, changing a variable or a list through a monitor does not change trigger project changed state.

Possibly also related to/blocking on scratchfoundation/scratch-gui#3652

Steps to Reproduce

For Variables:

1. Create a new variable 'foo'
2. Change the monitor mode for 'foo' to 'slider'
3. Click 'Save Now'
4. Change the value of the 'foo' using the slider
5. Observe that 'Save Now' does not appear in the menu bar.

For Lists:

1. Create a new list 'bar'
2. Click 'Save Now'
3. Add/Remove items in 'bar' using the plus/minus icons on the monitor.
4. Observe that 'Save Now' does not appear in the menu bar.