Discover: Leaves of disabled object fields are shown separately in the fields list

[flash1293]

Describe the bug: When the fields API is enabled, all leaves of enabled: false object types are shown as separate entries in the field list

Steps to reproduce:

1. Include something like this in the mapping:

"httpHeader" : {
          "type" : "object",
          "enabled" : false
        },

2. Ingest data like this:

"httpHeader" : [
            {
              "name" : "Accept",
              "value" : "nothing"
            },
            {
              "name" : "Cache",
              "value" : "not-available"
            }
          ],

3. Go to discover
4. All leaves are shown as separate fields

Expected behavior:
Just the object field itself is shown as field

Screenshots (if relevant):
7.11 (using _source):

master (using fields):

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

As discussed, closing this as working as expected.