Allow updating of barchart values (for use within `Live` scenarios)

[grofit]

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Is your feature request related to a problem? Please describe. I want to be able to update the value on a BarChartItem after it has been created, this is mainly for use cases when you want a chart to change in real time when using it within a Live scenario. As it stands at the moment even if I create each BarChartItem individually and access them the Value property is read only, with no set mechanism.

Describe the solution you'd like I want a way to be able to update the value within the barchart item after it has been initialized.

Describe alternatives you've considered Currently I just clear out all items and then just add them back in each time but it's inefficient

Additional context As mentioned this is mainly only useful within Live scenarios, but it feels like a useful addition.