Use activity icon when search suggestion icon is missing

New left-hand side icon fallback logic in search dialog:

1. If the search dialog gets no icon column, it shows no
   icon (like before). This would handle the case of in-app
   search where the provider does not include icons.
2. If the icon column is empty, or there is an error converting
   the icon id or URI to a drawable, the search dialog identifies
   the suggestion source by looking at the
   SUGGEST_COLUMN_INTENT_COMPONENT_NAME.
3. If SUGGEST_COLUMN_INTENT_COMPONENT_NAME is empty or not set,
   the current searchable activity is considered the suggestion source.
4. Try to get the activity icon of the suggestion source.
5. Fall back to the application icon of the suggestion source
   if there is no activity icon.
6. Fall back to some generic icon if there is no application icon.

Fixes http://b/issue?id=1905757