Changes in this CL:
1. 'exports' attribute renamed to roots
2. Removed restrictions for exporting a rule in a different repository
3. Kept restrictions for rules in the same repository but not in the same
package or subpackages
4. To get around restrictions, instead of the exported_by tag, one can use the
cc_shared_library_permissions rule
5. Added exports_filter that will match libraries in the transitive closure of
a root. Anything matched by the exports_filter will also be exported.
Restrictions as in 4. still apply.
RELNOTES:none
PiperOrigin-RevId: 310547916
Change-Id: I32d8e0d4dd4bcc9c9e92f4ff3c5b2a01564c31b2
8c31dd406c