Add Component source generator project

[Dreamescaper]

Contributes to #309 (2-4).

This PR has 4 commits, I suggests reviewing them one-by-one, ignoring whitespace changes.

1. Use Roslyn instead of reflection for Component Generator
   This commit updates ComponentWrapperGenerator project to use Roslyn instead of reflection. In order to be able to use Roslyn, I create Roslyn Workspace in Program.cs.
   I've tried to preserve the output exactly same as before, and to make as few changes as possible to ComponentWrapperGenerator.cs to make review easier.

2. Add Component source generator project
   In this commit I moved most of the generator classes to separate project Microsoft.MobileBlazorBindings.ComponentGenerator. I've added SourceGenerator class, which implements ISourceGenerator, and invokes ComponentWrapperGenerator for each required type.
   ComponentWrapperGenerator class is updated to return (string HintName, string Source) for generated files instead of writing them to disk.
   Source generator retrieves settings (namespace, types to generate) from 'component-generator.json' file in the project. Adding nuget dependencies to analyzers/source-generators is a bit troublesome, so I decided to parse json file using couple of regexes (at least for now, when json file is quite simple).
   Updated ComponentWrapperGenerator project to retain same functionality as before by adding reference to ComponentGenerator project and adding writing files to disk there.

3. Update generator to better support third party components
   Minor updates to ComponentWrapperGenerator class to better support third party components. Add missing usings, add alias for element's namespace. If generator does not know how to handle property type, and it is not ignored, then it fallbacks to AttributeHelper.ObjectToDelegate / AttributeHelper.DelegateToObject.

4. Add generator to Weather sample
   Add project Microsoft.MobileBlazorBindings.PancakeView.SourceGenerator, and use generator there to create component wrapper for PancakeView.
   Note that it is possible to use generator directly in Razor project, but it requires using .NET5 SDK, while MBB requires 3.1 (in global.json).

Naming is a bit confusing now - we have Source Generator project Microsoft.MobileBlazorBindings.ComponentGenerator (which should be published to nuget), and console project ComponentWrapperGenerator (for internal usage, at least for now).

Feel free to ask whatever questions you have!

Visual Studio screenshot