Repo / project restructurings

[zspitz]

Before:

• [x] Can visualizers be written using .NET Core 3? This would allow #80 without Costura, and #51
• [x] Can VS 2017 be supported this way? Do we need to?
  One possibility - multitarget .NET Framework and .NET Core; the .NET Framework version should be merged using Costura and packaged for VS 2017

ATM it seems that debugger-side dlls written in .NET Core for visualizers are not seen by Visual Studio. We'll have to do this in .NET Framework, and merge using Costura.

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During repo restructure:

• [x] Expression test objects
  • [x] separate project within repo
  • [x] add wiki page on ExpressionTreeToString
  • [x] wrap as nuget package (#89)
  • [x] project url should point to above wiki page
  • [x] trivially enables #88
• [x] move library into separate repo -> ExpressionTreeToString
  • [x] move Shared into ExpressionTreeToString
  • [x] use test objects library to run tests
  • [x] migrate to SDK project format; NRT
• [x] visualizer
  • [x] rename current repo, solution, projects to ExpressionTreeVisualizer
  • [x] remove Visualizer.2017; merge Visualizer.Shared and Visualizer.2019 into ExpressionTreeVisualizer
  • [x] migrate to SDK project format (#97); NRT
  • [x] split off debuggee code into separate projects
  • [x] build should go into separate subfolders based on target framework
  • [x] ZIP up all files, preserving this subfolder structure
  • [x] For .NET Framework debuggee, use Costura to merge into a single DLL
  • [x] Check the possibility for other debuggee versions
  • [x] create solution for CI; will build and run tests but not the "playground" projects; modify appveyor.yml
  • [x] create a post-build project in the original solution, not the CI solution; copies the output DLLs to the relevant folders
  • [x] merge library dll using Costura
  • [x] use test objects library to run tests
• [x] migrate wiki to new repos
  • [x] add changelog, roadmap, solution structure, and contributing pages
• [x] remove files from old repo; add links to new repos

After:

• [x] visualizer
  • [x] separate ExpressionTreeControl (displays viewmodel) from VisualizerWindow (manages DataContext using TransferData)
  • [X] break dependency of Package project on Visualizer project; reference shared projects directly
  • [x] MVVM, then #79 can be done using the test object library
  • [X] deploy viewmodels + views (including serialization models) as Nuget package
  • [ ] move all the code to a .NET Core 3.1 project (UI.Core); modifications made to this project
  • [ ] add a post-build step to copy all files into UI.Fx targeting .NET Framework
  • [X] ideally, multitarget .NET Framework, .NET Core (.NET Standard?)
  • [ ] remove dependency on MultiSelectTreeView
  • [x] create separate build output for VS 2019 -- ZIP file with subfolder structure for multiple frameworks -- and VS 2017 -- ZIP file with single dll
• [ ] Update external links -- RubberDuck, MS docs
  • [ ] https://github.com/agileobjects/ReadableExpressions/issues/47

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Some more details:

domains:
serialization models
visualizer object source
view models + views
visualizer

visualizer:
serialization models into multitarget debuggee dlls
everything else into NET Framework debugger dll
    reference to some debuggee dll is required, for use of serialization models

wpf control library:
(deploy as nuget package)
serialization models + view models + views
    constructor for view model from actual type (not serialization model)

test projects reference wpf control library
    (it will have a dependency on WPF, use .NET Core 3)

[zspitz]

PR for MS Docs is here.