Improve Design-Time Builds for Binding Projects

[jonathanpeppers]

Steps to Reproduce

1. Clone this sample: https://github.com/xamarin/XamarinComponents/tree/master/Android/ARCore/samples
2. Perform a design-time build (command line would be something like msbuild /t:Compile /p:BuildingInsideVisualStudio=True /p:DesignTimeBuild=True)
3. Look how slow it is...

On my machine, the DTB was taking over 16 seconds! Needless to say, we could improve this.

Expected Behavior

I think DTBs within Visual Studio are supposed to be under 500ms? maybe it was 250ms? Anyhow, way less than 16s!

Actual Behavior

DTBs take quite some time.

Version Information

I was using VS 2017 15.8.7 when I saw this.

Log File

Here is an example binlog:
msbuild.zip