feat: whitespace and message ordering configurations for #guard_msgs

[kmill]

Adds options to control whitespace normalization and message ordering in #guard_msgs.

Examples:

1. #guard_msgs (whitespace := lax) ignores differences in whitespace completely.
2. #guard_msgs (whitespace := exact) requires an exact match for whitespace (after trimming).
3. #guard_msgs (ordering := sorted) sorts the list of messages, to make it insensitive to message order.

[digama0]

The code action also needs to be modified to take the ordering := sorted setting into account, or else it will suggest a docstring that will fail the command.

[kmill]

@digama0 It's now about ready to come out of draft state. If you approve, then I'll go and create a PR for the first commit (bc75d48), then update stage0, and then this PR will just be for the third commit.

It turns out the code action didn't need special handling since the sorted version is passed into the info tree. I tested it by using it to create the docstrings in the test file.

[kmill]

@digama0 The staging business is all worked out now in this PR, and it's set to trigger a stage0 update after it merges.

[digama0]

Okay, LGTM. Let's see if merging works...

[Kha]

#guard_msgs (ordering := sorted) sorts the list of messages, to make it insensitive to message order.

Should this be considered a workaround for #2335?

[kmill]

@Kha Yes, though it goes a little further since, for example, a tactic might spawn multiple threads and report multiple messages nondeterministically at the same source position.