[libTooling] Move RewriteRule include edits to ASTEdit granularity.

Currently, changes to includes are applied to an entire rule. However,
include changes may be specific to particular edits within a rule (for example,
they may apply to one file but not another). Also, include changes may need to
carry metadata, just like other changes. So, we make include changes first-class
edits.

Reviewed By: tdl-g

Differential Revision: https://reviews.llvm.org/D85734