PATCH incorrectly replaces entire complex object

[jasonfagerberg-toast]

The DefaultPatchHandler incorrectly replaces omitted fields with null for complex objects such as name.

For the given request

{
  "schemas": [
    "urn:ietf:params:scim:api:messages:2.0:PatchOp"
  ],
  "Operations": [
    {
      "op": "replace",
      "path": "name",
      "value": {
          "givenName": "New Given Name"
      }
    }
  ]
}

the expected output should be

{
    "givenName": "New Given Name",
    "familyName": "Existing Family Name"
}

However, DefaultPatchHandler replaces familyName with null

{
    "givenName": "New Given Name",
    "familyName": null
}

I believe this is because DefaultPatchHandler.applySingleValue is replacing User.name with the entirety of the request instead of merging the existing with the request

According to the SCIM RFC

o If the target location specifies a complex attribute, a set of
sub-attributes SHALL be specified in the "value" parameter, which
replaces any existing values or adds where an attribute did not
previously exist. Sub-attributes that are not specified in the
"value" parameter are left unchanged.

[jasonfagerberg-toast]

Took a stab at fixing this #726

[bdemers]

Fixed in: #726