Add pop() and swap() to the Map trait #6236
                
     Merged
            
            
          
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Closes #5392 and #5393
I implemented the pop/swap methods for TrieMap/TreeMap/SmallIntMap, and I also updated all of them such that pop isn't just a remove/insert, but rather it's all done in one operation.
One thing I did notice is that with default methods it'd be really nice to define
insertandremovein terms ofpopandswap(or vice versa, just to have them available).