Rename $RTIRSearchResultFormats to %RTIRSearchResultFormats

Now you can actually use RT Config's built in hash merging of top level
keys, rather than copying the whole hashref and having problems when we
update the defaults that you didn't change or when we add new keys.
Nasty heuristic to warn about $RTIRSearchResultFormats

It ends up as the odd key in the %RTIRSearchResultFormats with a key of
the stringification of $RTIRSearchResultFormats and a value of undef,
so, warn in that case to help folks fix:

    Odd number of elements in anonymous hash at lib/RT/Config.pm line 1315.
    Odd number of elements in hash assignment at lib/RT/Config.pm line 1316.

Closes issues #30278
Merge branch '3.2/hashify-rtirsearchresultsformats'