Implements a new module, utop, as suggested in micropython/micropython#12732 (comment).

Currently only works on the esp32 port, and requires micropython/micropython#12732.

An animated GIF to demonstrate what the output looks like:

utop

Opted to give it a generic name instead of ESP32-specific, as there was mention of other platforms also having options to retrieve runtime performance data, which might be nice to support at a later time.

Compared to the version posted in that esp32 MR (here) this version is a few lines longer to make it a bit easier to read and expand later. For example it includes an optional argument for renaming threads, useful to distinguish multiple mp_thread instances.

First commit implements the functionality as demo'd in the other MR. The second commit adds two lines of information about the current state of the ESP-IDF heap, as an example of how we could expand this later to be a more useful development utility.