Reorganize samples

[giusepe]

What kind of change does this PR introduce?

Reorganization and clean-up, part of #781

What is the current behavior?

All samples are loaded from a single solution.

What is the new behavior?

Every sample has it's own solution, and some samples that were broken are now running again.

What might this PR break?

• While I did load and run one by one, maybe a sample can be broken
• Now sure how the bot that updates the libraries will be affected here

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
  There are no tests currently for these samples, so I tested them manually.

• Docs have been added / updated (for bug fixes / features)

Other information:

This is just a first pass, and more improvements are needed. However, I didn't want to make too many changes in one PR, so I've added a few comments to address later:

The Blazor samples are broken and super outdated, but I haven't removed them yet as I want to use them as a reference for creating new ones.
ClientSideExample
HostedExample.Client
HostedExample.Server

Samples that I kept but should be remade, or maybe removed:
Uno sample, we could use a better one.
Winforms demos, both are not running for me.
WPF Samples: ReactiveUI.Samples.Messaging and ReactiveUI.Samples.SideBySide.Caliburn: "Couldn't load the project"

I removed the MAUI sample because it was dependent on the Xamarin one and wasn't truly a MAUI sample; rather, it was more of a 'Xamarin written in MAUI' example.
I also removed Testing.SimpleViewModel since it wasn't worth keeping, as it is something we can include as part of the other samples.

[glennawatson]

Give me a day or so to go through this PR. Have some opinions where we should keep the mega solution somewhere but also keep all the new sub solutions.

Solution filters is likely a better fix over all these sub solutions btw.

[giusepe]

Take your time, no hurry.

TIL about the solution filters.

[glennawatson]

You can if you like. I won't get to it until the weekend regardless. Slnf are xml files btw so easy enough to generate if you want yourself

[giusepe]

Hey, happy holidays!

Now, I did some experimentation with the solution filters, creating a filter per "project" (Cinephile, MasterDetail, ReactiveDemo, etc).
Not sure if I'm doing something wrong, or if this expected, but using the filters still requires the installation of the SDKs used in the whole solution.

[glennawatson]

Happy to go forward with the sln approach. Sorry for taking so long to reply.

[giusepe]

Hey man, no worries.

I'll fix the merge conflict and proceed with the change.

[giusepe]

The conflicts are fixed and pushed.

Please, let me know if you spotted any mistakes or anything that you would like to be different.