Support bulk sharing of saved objects

[jportner]

As of this writing, data views and ML jobs are the only shareable saved object types in Kibana. In the future, more saved object types will become shareable (#128907) and some consumers want the capability to bulk-share saved objects.

The reusable "Share to space" flyout currently looks like this:

This flyout is focused on a single object, though the action of sharing/unsharing will also transparently affect any "related objects" (e.g., the entire outbound reference graph).

The server-side API already supports bulk-sharing objects, but there isn't currently a good way to represent this in the UI. Some issues:

1. Obviously the UI currently only displays the current object's title; that would have to be changed to represent that multiple objects are being changed.
2. The list of spaces shows which are already selected for the current object, and it allows the user to select new ones or deselect existing ones (to "share" or "unshare" the object). However, if multiple objects are being shared, it's likely that different objects will have a different set of existing spaces that they are shared to -- this is no longer a binary display, we would need some sort of "indeterminate" checked state to reflect that some of the objects are shared to a space already, but not all of them.
   @MichaelMarcialis and I suggested adding this functionality to EuiSelectable ([EuiSelectable] Add support for Indeterminate values eui#4668) but it was rejected. If we were to implement this, we would have to get rid of our usage of EuiSelectable and replace it with something custom.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)

[legrego]

Related to #52098