[One .NET] no longer produce .apk for IDE builds

[jonathanpeppers]

Related: #5436

In "legacy" Xamarin.Android, we have the following behavior:

1. The Build target does not produce an .apk or sign it.
2. Only SignAndroidPackage (or Install) would do this.

So if you hit F6, Ctrl+B, Command+B, etc. in Visual Studio, you don't
have to wait on a valid .apk file to be produced to get build
results. This is useful for incremental build performance -- and
developers' habit of hitting build all the time.

dotnet build has different behavior, because it should inherently
produce something that is runnable. dotnet build currently produces
an .apk file and signs it.

To match "legacy" Xamarin.Android's behavior in IDEs we could do
something different while in Visual Studio when
$(BuildingInsideVisualStudio) is set. This way we get the desired
behavior:

• dotnet build at the command-line produces a signed .apk file.
• IDEs will not produce an .apk on Build. However, when "deploy"
  occurs, the Install target will handle producing an .apk file as
  needed.

This allowed me to update the PerformanceTest that was adding
additional time under .NET 6 for producing .apk files. Our MSBuild
tests always set $(BuildingInsideVisualStudio) for testing.

I also updated the [Retry] attributes so the value was in one place.