Redesign --max_function_stack_trace_depth flag

[piotmag769]

This flag currently has a few issues:

• the name is inaccurate (the profile graph doesn't have to be a tree due to possible mutual recursion, so the word depth is misleading)
• simple recursive function calls are merged for the purpose of this flag, but mutually recursive function calls are not:
  • call stack [f, f, f, x, y, z] is merged to [f, x, y, z]. With the flag set to 3 the stack will be cut to [f, x, y] and the user will see a graph like this f -> x -> z
  • call stack [a, b, a, b, c, d] is not merged. With the flag set to 3 the stack will be cut to [a, b, a] and the user will see a graph like this

     a -> b-|
     ^------|
    

    without the c function
• a user has no option to disable merging of recursive functions (prob not in the graph/UI itself, just for the purpose of the depth flag) and (?) loop functions (this one is probably fine as loop functions should always be merged, but we can make a separate option for that) - probably another flag could be added

A design doc should be written.