convert gentracesources to tt

[stevenbrix]

This PR updates the WpfArcadeSdk to move our gentracesources.pl and gentracestrings.pl to using design time t4 generation. Instead of these files being generated into $(IntermediateOutputPath) they are now put under $(WpfSourceDir), and are easily discoverable in the project files.

There are a few caveats in order to get this to work:

1. We have to ensure BuildDependsOn variable that T4 targets update doesn't get overwritten. So with SDK style projects, we have to manually import the Sdk.targets and then include the T4 targets after.
2. I wanted to decouple the GenTraceSources and GenAvMessages (similar to how we had 2 separate perl scripts before). In order to do this, those targets can't include the T4 targets, since then you get MSBuild authoring errors about the same target being imported twice.

Below is an example of how WindowsBase uses these targets. PresentationFramework and PresentationCore are similar, only without the GenTraceSources.targets import.

  <Import Project="Sdk.targets" Sdk="Microsoft.NET.Sdk" />
  <Import Project="$(WpfCodeGenDir)AvTrace\GenTraceSources.targets" />
  <Import Project="$(WpfCodeGenDir)AvTrace\GenAvMessages.targets" />
  <Import Project="$(WpfCodeGenDir)DesignTimeTextTemplating.targets" />

There will be an internal PR that shows how these changes are consumed. The goal here is that we will continue to move more and more of our codegen scripts to T4 templates, where we should be able to use this as a starting point for completing that work.

[vatsan-madhavan]

Nice! Need a little time to review - will get to as soon as possible after working through some preview 5 deliverables.

Would be great to get @rladuca's input as well.

[rladuca]

This looks good, just some spelling/wording nits.

As a general suggestion, the comments you spit out in the T4 for some functions/properties should be XML style "///" comments.

[rladuca]

"Importing Sdk.Targets because it needs to be imported after Sdk.Targets" is phrased oddly.

I think what you want to say is more like "Microsoft.TextTemplating.targets needs to be imported after Sdk.Targets, therefore Sdk.Targets must be manually imported."

[rladuca]

Also SDK.Targets probably should be in backticks as well.

[stevenbrix]

Rewording to:

When using the SDK-style project format, including the Microsoft.TextTemplating.targets requires us to manually import Sdk.Targets because the BuildDependsOn variable, which is modified by the T4 targets, would otherwise be overwritten by the automatic inclusion of Sdk.targets