Public link resharing permissions

[fschade]

Describe the bug

a user is able to create a public link as an editor even if he only has viewer permissions for the incoming share

Steps to reproduce

1. user a shares a resource to user b as viewer
2. user b creates a public link of the share with editor permissions

Expected behaviour

the backend does not allow to create public links with higher permissions then the user has

Current behaviour

the backend allows the creation

[phil-davis]

Similar to #3881

https://github.com/owncloud/ocis/blob/master/tests/acceptance/expected-failures-API-on-OCIS-storage.md has:

#### [Increasing permission of a public link of a folder that was initially shared with share+read permissions is allowed](https://github.com/owncloud/ocis/issues/3881)

- [apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature:159](https://github.com/owncloud/core/blob/master/tests/acceptance/features/apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature#L159)
- [apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature:160](https://github.com/owncloud/core/blob/master/tests/acceptance/features/apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature#L160)
- [apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature:181](https://github.com/owncloud/core/blob/master/tests/acceptance/features/apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature#L181)
- [apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature:182](https://github.com/owncloud/core/blob/master/tests/acceptance/features/apiSharePublicLink2/reShareAsPublicLinkToSharesNewDav.feature#L182)

There are failing API tests that cover this problem.

[micbar]

duplicate of #3881 which has already a P2 and is on the board

[kobergj]

cs3org/reva#3023