Support changing the active stack frame in CLI debugger (node inspect)

[jkrems]

See #14049

[jkrems]

From the original thread:

There's no official/documented way of doing it right now. Some things that work but definitely need some cleanup and an official interface:

debug> bt[2].list() // list source context for frame at index 2
debug> bt[2].loadScopes() // show the scope chain w/ values for the frame nodejs/node-inspect#2

Things that do not exist in any form yet: Eval on a specific stack frame or changing the selectedFrame.

[TimothyGu]

Does the original node debug support changing stack frames? If so we should implement it in a way that's close to it.

[jkrems]

Afaict the previous debugger didn't support switching frames either (currentFrame couldn't be modified). So the interface is pretty open.