mapWithAdditionalDependencies from FSAC.

[TheAngryByrd]

@krauthaufen and I have been going back and forth on things that have helped the implementation of using FSharp.Data.Adaptive in FsAutocomplete.

One of the weird use cases is loading and noticing changes to fsproj files with msbuild. We need to re-execute retrieving msbuild project data on every change to an fsproj file. However there are additional files that may change during editing code that isn't immediately knowable until you've already executed msbuild (such as project.assets.json). When those dependent files change, (due to a something such as dotnet restore), we also need to re-execute getting information from msbuild for that project. @krauthaufen helped craft the AVal.mapWithAdditionalDependencies.

The only problem with the implementation was on any change we would want to reload the whole solution which can take longer the more projects that are involved. We can be a bit smarter and reload only the projects that need it. We could do this one at a time with the current offering in AMap but this would also be extra overhead. It would be nicer to operate in batches, so if multiple projects need reloaded, we only call out to msbuild once. BatchRecalculateDirty will rerun the mapping function for any new inputs from a reader and any dirty ones InputChangedObject.

I do have a working implementation over in ionide/FsAutoComplete#1082.

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@krauthaufen also mentioned creating implementations for ASet and AList, but I wanted to get the ball rolling on some feedback. I'm not tied to these names, if there's better ways to convey the semantics on this or better implementations of what I'm doing, I'm all ears.

[krauthaufen]

Maybe just call it batchMap?

Great comtribution, btw.