creating a `BacktraceFrame` from `Frame`

[Glauber Costa]

Hello

I am writing some code that would acquire a backtrace from a no-std environment (a signal handler). Therefore, I capture manually with trace_unsynchronized.

However, that's the only part of the process that needs to be nostd: after the backtrace is captured I can send it for later processing, at a time in which I have std.

It is pretty inconvenient to print the result, though, as a BacktraceFrame cannot be created from a Frame, and all the pretty printers require a BacktraceFrame.

Would it be possible to have a From implementation that converts them ?