BUG #14888: Fix state loading errors.

BUG #14888 was showing up for the following reasons:

The saved XML state had save values for the  "ColorArrayName" property's
domain for the Sphere's representation. When the state was loaded, since
vtkSMStringListDomain overloaded the LoadState() method, it read the values from
the XML state. Now, since the state didn't save information about array
association, when the state was loaded, naturally, vtkSMArrayListDomain subclass
for this domain didn't have sufficient state and hence when UI tried to get
information about the arrays, it raised errors.

The problem stemmed from the fact that we shouldn't be reloading state for
domains from XML (except ProxyListDomain). Domain values are either compile time
(specified in server manager configuration XML) or run time (determined by run
time data values). For both cases, loading from XML state doesn't help at all.

Fixed this and update vtkSMDomain to have documentation to keep developers from
overriding LoadState() accidentally.

Change-Id: I729df876c3762b2a05d8f95a1f8a20ed97359a7d
BUG #14889. Fixed pqDisplayColorWidget for values not in domain.

Fixed pqDisplayColorWidget to properly handle the case when the values
for the SMProperty are not in the domain. This change also ensures
that whenever the domain is updated with relevant information, the UI
will also update to show most up-to-date information  about component
available, and the selected component.

Also added a test (LoadPartiallyUpdatedStateFiles) which tests both,
BUG #14888 and BUG #14889.

Change-Id: Id0488f0e024b7580aea5ef687f4efcd486ced400
Merge topic '14888_fix_state_loading_for_domains' into next

48d829b7 BUG #14889. Fixed pqDisplayColorWidget for values not in domain.
cf306d20 BUG #14888: Fix state loading errors.