Debugger inspect should not collapse when stepping

[jwunderl]

Is your feature request related to a problem? Please describe.

In the debugger, collapsing the variable inspect view each time you step is annoying when you step through a program

Describe the solution you'd like

Should keep any variables that are expanded open when stepping through a program, so you don't have to keep on re-inspecting the same thing

Describe alternatives you've considered

n/a

Additional context

split off from https://github.com/microsoft/pxt-arcade/issues/1252