Add preview support in CsStackView

[its-izhar]

I use cscope_maps quite frequently and it's an amazing plugin. Been using it for a while now with telescope picker.

I wanted to request for a feature to enhance CsStackView to display preview with the chosen picker. As it is, CsStackView command is pretty useful to quickly familiarize yourself with the call hierarchy, especially with a new codebase. Adding the ability to display a "grep preview" side by side to the call tree would be super helpful to understand the context around the code.

Please consider this, it would be a good value add to this amazing plugin.

Thanks!