Remove support for coalescing progress reports in LLDB. This
functionality was motivated by Xcode, which wanted to listen for less
frequent, aggregated progress events at the cost of losing some detail.
See the original RFC [1] for more details. Since then, they've
reevaluated this trade-off and opted to listen for the regular, full
fidelity progress events and do any post processing on their end.

rdar://146425487

This patch adds a finalize method which destroys the underlying RAII
SBProgress. My primary motivation for this is so I can write better
tests that are non-flaky, but after discussing with @clayborg in my DAP
message improvement patch (#124648) this is probably an essential API
despite that I originally argued it wasn't.

This fixes the obvious, but untested case of sending None/Null to
SBProgress. 

Recently I've been working on a lot of internal Python tooling, and in
certain cases I want to report async to the script over DAP. Progress.h
already handles this, so I've exposed Progress via the SB API so Python
scripts can also update progress objects.

I actually have no idea how to test this, so I just wrote a [toy command
to test
it](https://gist.github.com/Jlalond/48d85e75a91f7a137e3142e6a13d0947)


![image](https://github.com/user-attachments/assets/7317cbb8-9145-4fdb-bacf-9864bf50c467)

I also copied the first section of the extensive Progress.h class
documentation to the docstrings.