iOS parity, fetch control, and deprecation notice updates for mobile docs

[jaredlockhart]

Follow-up to #786. Several smaller gaps in mobile SDK docs:

• iOS integration guide missing recordMalformedConfiguration() (added to Android in docs: update mobile SDK integration guides to match current source #787 but not iOS)
• setFetchEnabled() / isFetchEnabled() QA methods undocumented in mobile-ui.md
• Deprecated custom-targeting docs on both platforms don't link to the new recordedContext builder option