Manifest root range needs viewing hint to render properly in Mirador

[mspalti]

Describe the bug
This bug was originally described in DSpace/dspace-angular#1395 because it causes a display issue in the Mirador viewer. However, the update is required on the REST side since it's caused by an omission in the IIIF manifest. I am recreating the issue here.

Currently, the table of contents view does not include the "top" viewing hint. From the docs:

[top viewing hint] Valid only for ranges. A Range with this viewingHint is the top-most node in a hierarchy of ranges that represents a structure to be rendered by the client to assist in navigation. For example, a table of contents within a paged object, major sections of a 3d object, the textual areas within a single scroll, and so forth.

Without this viewing hint, the Mirador viewer displays redundant information: an expandable "table of contents" element that includes all ranges and the same ranges listed separately.

To Reproduce
In the Mirador viewer, choose the index (in the left navigation panel) for this test item:

https://digitalcollections.willamette.edu/items/0a53d851-319b-4883-9d80-6bf0148ee2ed

Expected behavior
There should be a list of all ranges, with the redundant table of contents hidden.

The manifest should include the viewingHint:

{ @id: "https://digitalcollections.willamette.edu/server/iiif/0a53d851-319b-4883-9d80-6bf0148ee2ed/manifest/range/r0", @type: "sc:Range", label: "Table of Contents", viewingHint: "top", },