Can be change DraggableScrollableSheet initialChildSize

[cnkygmr]

I want to adjust the height that comes at the beginning. The user can increase it if he wants. For example, if the maximum is 0.9, I want the length to come at the beginning as 0.4.

[cnkygmr]

Or we should be able to set all the values If we do not give a value, the standard one will be used by default.

      initialChildSize: maxChildSize,
      maxChildSize: maxChildSize,
      minChildSize: _sheetProvider.minExtent,

[LegendAF]

I'll dig into this as soon as I can this week. Thanks for the ticket!

[LegendAF]

@cnkygmr This turned out to be a bit bigger than expected. I have a path forward and I will have a PR up within the next couple days.