Updated State of Valhalla docs

[Brian Goetz]

I've updated the first two State of Valhalla docs to the latest design, 
and staged them in their new repo.  They can be viewed here:

https://github.com/openjdk/valhalla-docs/blob/main/site/design-notes/state-of-valhalla/01-background.md

https://github.com/openjdk/valhalla-docs/blob/main/site/design-notes/state-of-valhalla/02-object-model.md

Though, these are not their permanent homes, and there are several what 
appear to be formatting errors, which are artifacts of the skew between 
pandoc markdown and github markdown.  Still working on infra to properly 
format and push to the OpenJDK website, which will be the real home for 
these docs.