Outliner freezes when searching in large maps

This is because SSceneOutliner::FullRefresh is called every time the search text changes, which repopulates the whole tree.

There's a few options to look into here (first two might be tricky with backwards compat to consider):

• Time-slice the repopulation
• Parallelize the search
• Track down what part of the refresh takes the longest and look for low hanging optimizations
• Update the search logic to not refresh immediately on every character typed
• Update the search logic to dynamically look for updated results instead of doing a full refresh

1. Launch the editor and open any large world partition map
2. Start typing letters into the Outliner to search

Note that on really large maps, the Outliner hitches after you type each character. This is because a full synchronous refresh happens to gather the search results every time you type a single character.