Currently, the words "buffer", "node" and "element" are used together in G1SegmentedArrayXxx, G1CardSetXxx and related classes in an inconsistent way, which is very unfavorable for understanding.

We should not confuse buffer and node together, and not confuse node and element together. The new wording should be based on something like the following rule:

segmented array (1) -- segment (N) -- slot (M)