Rename BlockedSlice from #459 to NoncontiguousBlockSlice

[mtfishman]

This PR is split off from #462, it renames BlockedSlice introduced in #459 to NoncontiguousBlockSlice and also adds more functionality and tests so that it is as featureful as BlockSlice. The reason for the name change is that in #462, this type will be used in slicing operations such as V[[Block(1), Block(3)]] and V[Block(1)[[1, 3]]]. In my opinion, BlockedSlice doesn't make a lot of sense as a name for the latter case. The more general concept is that it is a slice object constructed when there is a non-contiguous blockwise slice of some form (either non-contiguous blocks or non-contiguous within a block).

I'm open to other name suggestions, NoncontiguousBlockSlice is the best I could come up with and there isn't really an analogous case for this in Base from what I've seen. Note the main reason why we can't just use BlockSlice for those cases is that BlockSlice is an AbstractUnitRange subtype and NoncontiguousBlockSlice covers cases where the slices aren't ranges, so maybe BlockSliceVector could work as a name to emphasize that point.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (cc5eb23) to head (bb4ae8f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #479      +/-   ##
==========================================
+ Coverage   94.48%   94.50%   +0.01%     
==========================================
  Files          19       19              
  Lines        1778     1783       +5     
==========================================
+ Hits         1680     1685       +5     
  Misses         98       98              

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[dlfivefifty]

Can you get the codecov up?

[mtfishman]

Can you get the codecov up?

Yes, will do.