Update Recipe Robot to support/replicate SparkleUpdateInfoProvider current version detection capabilities

[PeetMcK]

Is your feature request related to a problem? Please describe.
Recipe Robot's logic for discovering 'version' from a Sparkle appcast url does not behave the same as SparkleUpdateInfoProvider and consequently adds a redundant Versioner processor to [AppName].download.recipe

Describe the solution you'd like
I may be mistaken, but RR is only looking for app version info in the appcast xml enclosure, and when it's not found it downloads the most recent url, and adds a Versioner processor to discover the app version. Version discovery was updated in SparkleUpdateInfoProvider with this change: autopkg/autopkg#841. Versions found outside of enclosure are respected and now used.

Adding the same behavior to RR as was added to SparkleUpdateInfoProvider in autopkg/autopkg#841 would allow RR to pull the same version info as SparkleUpdateInfoProvider and should stop RR from creating redundant Versioner processor steps in [AppName].download.recipe.

If the updated logic in RR does not find a version anywhere in the appcast xml it should not create a recipe using the SparkleUpdateInfoProvider as any appcast xml with no version should fail to download. As it did when the SparkleUpdateInfoProvider was only looking in enclosure for version info... autopkg/autopkg#839

Describe alternatives you've considered
Keeping the logic that adds a Versioner processor to a Sparkle download recipe. However, if the Versioner processor is required, SparkleUpdateInfoProvider should already fail to download the app in the first place.

Additional context
Just thanks for your continued work on RR! It's a huge help maintaining my autpkg/munki.