Bug 13061 – [GC] investigate using compressed bitmaps for attribute bits

We're currently using a considerable amount of space storing bitmaps. I suspect the bit patterns within them are good candidates for compression. The attributes which aren't aren't used during marking inner loop are good candidates for compression as they are less performance sensitive. There's even room for improvement with the eagerly allocated "scan" bit set which are only used for deferred scanning of blocks when a deep heap graph is encountered.

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