restrict: only return OffsetArray when input is an OffsetArray

[johnnychen94]

Unless people's code depends on the array container type (e.g., out.parent), this isn't a breaking change.

img = rand(4, 4)
restrict(img)
# master: 1-based OffsetArray
# PR: Array

img = OffsetArray(rand(4, 4), -1, 0)
restrict(img) # behavior not changed

Also, add some more tests on the property.

[codecov]

Codecov Report

Merging #4 (b5d2626) into master (eff14e9) will increase coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #4      +/-   ##
==========================================
+ Coverage   94.73%   95.08%   +0.34%     
==========================================
  Files           1        2       +1     
  Lines         114      122       +8     
==========================================
+ Hits          108      116       +8     
  Misses          6        6              

Impacted Files	Coverage Δ
src/compat.jl	100.00% <100.00%> (ø)
src/restrict.jl	95.04% <100.00%> (+0.30%)	⬆️

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[johnnychen94]

Actually, this 1-based OffsetArray output is introduced by the instability fixes: JuliaImages/ImageTransformations.jl#124.

It's not yet released, so I'm relieved that this unexpected change gets reverted.

[timholy]

It would be better not to specialize on OffsetArray, because it's far from the only special array type in the universe. similar , supplied with appropriate axes for the result, should allocate the correct type for us. What's needed is a correct way to compute the axes of the returned value.