This adds a basic SB API for creating and stopping traces.
Note: This doesn't add any APIs for inspecting individual instructions. That'd be a more complicated change and it might be better to enhande the dump functionality to output the data in binary format. I'll leave that for a later diff.
This also enhances the existing tests so that they test the same flow using both the command interface and the SB API.
I also did some cleanup of legacy code.
Differential Revision: https://reviews.llvm.org/D103500
Create a "Design" section for the LLDB documentation. The goal is to
have design documents that describe how the LLDB internals work.
Currently similar pages are mixed together under the "Development". The
existing pages describing the architecture, the reproducers, the
structured data plugins, and the SB API could be housed here. I hope
we'd see more pages being added here in the future.
Differential revision: https://reviews.llvm.org/D88516