Move ForwardingPolicyProvider, etc. to components/policy/.

Depends on https://codereview.chromium.org/92263002/

BUG=271392

Review URL: https://codereview.chromium.org/92133003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238697 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238697