Add border spacing and fixed cell height to grid.
- Border spacing is the spacing between the cells.
- Workspace cell height is now fixed, and we allocate
all the "extra" space to three different variable height
areas.
* Built behind ENABLE_FOUR_COLUMNS flag because it hinders the
default grid.
Bug: 175329686
Test: - set border spacing to 0 and confirm matches prior layout
- test drag and drop still worked
- test reordering
- test widgets
- test folders
- test multiwindow
Change-Id: Ic6f3dff577d28ff214bda4b0a787ec7fd08c108b
14 files changed