Expand local variables by default

[mvtec-richter]

Feature Description:

When using the debugger in Theia, the first thing I need to do is to expand the local variable scope to see the values of the local variables of the current scope. This is annoying, as this has to be done every time I start debugging again.
The should expand the local variables by default.
VSCode does this too.

[mvtec-richter]

I already looked into the implementation and saw, that initial state of expanding is set here:
https://github.com/eclipse-theia/theia/blob/master/packages/core/src/browser/source-tree/source-tree.ts#L67
Unfortuately, it's always initialized with false.
I wonder, if it would be ok to add a boolean property expandByDefault to CompositeTreeElement and use this in the toNode method?

[JonasHelming]

@rschnekenbu