SSTableRewriter opens all sstables as early before completing the compaction

In CASSANDRA-8320, we made the rewriter call switchWriter() inside of finish(); in CASSANDRA-8124 was made switchWriter() open its data as EARLY. This combination means we no longer honour disabling of early opening, which is potentially a problem on windows for the deletion of the contents (which is why we disable early opening on Windows).

I've commented on CASSANDRA-8124, as I suspect I'm missing something about this. Although I have no doubt the old behaviour of opening as TMP file reduced the window for problems, and opening as TMPLINK now does the same, it's not entirely clear to me its the right fix (though it may be) since we shouldn't be susceptible to this window anyway? Either way, we perhaps need to come up with something else, because this could potentially break windows support. Perhaps if we simply did not swap in the TMPLINK file so that it never actually get mapped, it would perhaps be enough. JoshuaMcKenzie, WDYT?