Don't prompt user to choose conflicting modules

[HebaruSan]

Problem

A module that tries to filter an option out of the "Too many mods provide" prompt with a conflict just ends up complaining to the user after the fact:

depends:
  - name: CustomBarnKit
conflicts:
  - name: CustomBarnKit-RO

$ ckan compat add 1.7
$ ckan install Komplexity
Module CustomBarnKit is provided by more than one available module. Please choose one of the following:
1) CustomBarnKit-RO (Custom Barn Kit - RO build)
2) CustomBarnKit (Custom Barn Kit)
Enter a number between 1 and 2 (To cancel press "c" or "n".): 
1
The following inconsistencies were found:
* CustomBarnKit-RO 1.1.20.0 conflicts with Komplexity 0.9.3.0
Install canceled. Your files have been returned to their initial state.

Noticed while investigating KSP-CKAN/NetKAN#8656.

Cause

The relationship resolver relies on AvailableModule.Latest to generate the modules for the user prompt, which filters modules with AvailableModule.DependsAndConflictsOK, which only checks conflicts unidirectionally.

Changes

Now AvailableModule.DependsAndConflictsOK checks conflicts bidirectionally, so choices that the installing modules conflict with will be filtered out before (or without) prompting:

$ ckan compat add 1.7
$ ckan install Komplexity
About to install:

 * Komplexity 0.9.3.0 (cached)
 * Module Manager 4.2.1 (cached)
 * Custom Barn Kit 1.1.21.0 (cached)
 * Kerbal Changelog v1.4.2 (cached)

Continue? [Y/n]

Concerns

This will probably pre-empt the "{conflicting_mod} conflicts with {candidate}" message in other cases, which might be confusing. I need help identifying those cases so I can figure out how to address them. Are there other situations where a mod might depend on its own conflict?

[DasSkelett]

This will probably pre-empt the "{conflicting_mod} conflicts with {candidate}" message in other cases, which might be confusing. I need help identifying those cases so I can figure out how to address them. Are there other situations where a mod might depend on its own conflict?

I can't come up with a situation where this would make problems, and testing with some mods with more complex relationships (Scatterer with its self-conflicts, RP-1 Express Install) worked fine.

So if this introduces a bug in the resolver, at least it won't hit too hard 😅

[DasSkelett]

The changes do make sense in theory, let's see if they withstand in practice 🤞