[workload] move all build tasks out of library-packs

[jonathanpeppers]

Description of Change

Fixes: https://dev.azure.com/devdiv/DevDiv/_workitems/edit/1459138
Fixes: #4098

This partially reverts 974cac4.

Creating a new MAUI solution, results in several intellisense errors:

CS0103: The name 'InitializeComponent` does not exist in the current context.

The missing members are created by the (previously XamlG) Roslyn
source generator. You can go-to definition the missing members, build
& run works, and if you close/reopen the solution the errors go away.
Unchecking the Run code analysis in a separate process, also seems
to solve the issue.

.NET MAUI seems to be using an intersection of features that causes
this problem:

1. We have a dotnet new maui project template.
2. We have a source generator in a NuGet package.
3. We have MSBuild targets that setup the source generator in a NuGet
   package.
4. We use AdditionalFiles to pass .xaml files in to the source
   generator.

What happens on the first project load, the design-time builds
before project restore are missing the source generator. So the call
to <Csc/> does not have @(Analyzer) or AdditionalFiles at all.

To solve this issue, we can move everything out of NuGet packages,
so they become regular "SDK" or workload packs:

• Microsoft.Maui.Controls.Build.Tasks is no longer packable
  • all files moved to Microsoft.Maui.Sdk
• Resizetizer.csproj is no longer packable
  • actual files are in Microsoft.Maui.Resizetizer.Sdk
• $(MauiVersion) no longer applies to build tasks

Testing locally, this seems to solve the problem for me. I can see the
@(Analyzer) and AdditionalFiles being passed on all design-time
builds now.

Other changes:

• I added %(IsImplicitlyDefined) to the source generator assembly. I
  just noticed this was missing while reading .binlog files.
• I put all files in the Sdk folder in Microsoft.Maui.Sdk. This
  seems a bit simpler to have one directory.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)
• Targets a single property for a single control (or intertwined few properties)
• Adds the property to the appropriate interface
• Avoids any changes not essential to the handler property
• Adds the mapping to the PropertyMapper in the handler
• Adds the mapping method to the WinUI, Android, iOS, and Standard aspects of the handler
• Implements the actual property updates (usually in extension methods in the Platform section of Core)
• Tags ported renderer methods with [PortHandler]
• Adds an example of the property to the sample project (MainPage)
• Adds the property to the stub class
• Implements basic property tests in DeviceTests

Does this PR touch anything that might affect accessibility?

No

[jonathanpeppers]

So I went through the nightmare of installing the packs from CI:

1. I started with 17.1 Preview 3, the MAUI workload from VS.
2. Delete C:\Program Files\dotnet\metadata\workloads\6.0.200\installertype\msi
3. signtool remove /s "C:\Program Files\dotnet\sdk\6.0.200-preview.22055.15\dotnet.dll"
4. Download the nuget artifact and put all *.nupkg files in C:\src\maui\artifacts
5. Install workloads from maui/main: dotnet workload install maui --from-rollback-file https://aka.ms/dotnet/maui/main.json --source https://aka.ms/dotnet6/nuget/index.json --source https://api.nuget.org/v3/index.json
6. Install the local .nupkg files on top: dotnet build src/DotNet/DotNet.csproj -t:Install

It works!