Introduce the Windows lcow diff/snaphotter

Implements the Windows lcow differ/snapshotter responsible for managing
the creation and lifetime of lcow containers on Windows.

Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>

platforms/defaults.go

@@ -22,11 +22,6 @@ import (
 	specs "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
-// Default returns the default matcher for the platform.
-func Default() MatchComparer {
-	return Only(DefaultSpec())
-}
-
 // DefaultString returns the default string specifier for the platform.
 func DefaultString() string {
 	return Format(DefaultSpec())