More info: https://github.com/microsoft/vscode/issues/76909#issuecomment-524976250

fixes #71407

Fixes #79781

* add deserialization to splitview

* add new grid deserialization test to index.html

* working mostly

* branchnode should invert orthogonality in splitview

* fix issue with sidebar snapping

* cleanup and make splitview api more explicit

* hook up children sash reset

* adopt single deserialize (PR feedback)