[SR-8971] Expose the REPL/SwiftREPL LLDB classes through the SB Python API

[pvieito]

Previous ID	SR-8971
Radar	rdar://problem/45217698
Original Reporter	@pvieito
Type	New Feature

Additional Detail from JIRA

Votes	0
Component/s	LLDB for Swift
Labels	New Feature
Assignee	None
Priority	Medium

md5: 26b1e6db75851f3854e3d3732eb2a0f8

Issue Description:

As commented in the Swift Forums (https://forums.swift.org/t/jupyter-kernel-launch-the-debugger-with-the-current-triple-in-repl-mode)) this API would be very useful for implementing LLDB-based REPLs from a Python environment (like a Jupyter kernel).

[AnnaZaks]

@swift-ci create

[marcrasi]

I have started looking closer at this, and I now think that the REPL / SwiftREPL is not the right abstraction to expose through the SBAPI. The REPL / SwiftREPL handles a bunch of commandline UI stuff that is not relevant for a consumer like Jupyter that implements its own UI.

For example, `SwiftREPL::CompleteCode` returns completions in a way that is very specific to how the commandline works (when there is 1 completion, it returns an insertable string so that the UI can insert the text; when there are >1 completions, it returns more detailed "displayable" completions that can't be inserted directly into code because they have type information). The ideal completion API for a consumer like Jupyter would always return some structured data with both "insertable" and "displayable" completions, so that the Jupyter UI can decide what to do with them.

I'm going to try adding a completion function to the SBAPI that is independent from the SwiftREPL completer. This SBAPI completer will return structured completion data.