internal/xds: change xds_resolver to use dependency manager (#8711)

internal/xds: change xds_resolver to use dependency manager (#8711)

This change is part of
[A74](https://github.com/grpc/proposal/blob/master/A74-xds-config-tears.md)
implementation.

This PR removes the listener and route watchers from resolver and
changes it so that we get the resources from xds dependency manager.

RELEASE NOTES:
* xds/resolver:
* Changes the behavior such that getting no matching virtual host in a
route resource will now drop any previous resource and report the error.
* Changes the behavior so that receiving a configuration error (LDS/RDS
ambient error) after a successful update will now only be logged, and
the system will continue using the previous resource to avoid transient
channel failures