Define Base.axes1(S::Base.Slice{<:BlockedOneTo})

[mtfishman]

Define Base.axes1(S::Base.Slice{<:BlockedOneTo}) = S.indices, analogous to the definitions Base.axes(S::Base.Slice{<:BlockedOneTo}) and Base.axes1(S::Slice{<:Base.OneTo}).

Closes #484.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.04%. Comparing base (a4a0b93) to head (021dc7b).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #487      +/-   ##
==========================================
+ Coverage   93.81%   94.04%   +0.23%     
==========================================
  Files          19       19              
  Lines        1761     1764       +3     
==========================================
+ Hits         1652     1659       +7     
+ Misses        109      105       -4     

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