[Java.Interop.Tools.Cecil] Change DirectoryAssemblyResolver to allow forced loading.

[dellis1972]

Context dotnet/android#1154

One of the problems we currently face is that our build system
resolves ref netstandard libraries. With the current cache
system, onces an assembly has been loaded into the Cecil cache
it only ever uses that assembly. We might need to replace the
current cached version with a new one if we detect a ref and
need to reload the lib.

[jonpryor]

I don't fully understand how this will be used in xamarin-android. This patch implies that "someone" will call DirectoryAssemblyResolver.Load(fileName, forceLoad:true). Who is that someone, and how are they going to obtain the second assembly to load? How will we ensure that the second assembly we're loading is in fact the correct assembly, so that we don't inadvertently replace the "real" assembly with the "reference" assembly? (If we can ensure that, then why not just do that in the first place? Then forceLoad wouldn't be needed.)

This patch raises more questions than it answers.

Then there's more thought-provoking material.