Add virtual properties for values and indices

[mkitti]

This is a full implementation of #316. Virtual properties for values and indices are added and documented.

This differs from the proposed implementation in #316 in that the properties return IdOffsetArray rather than UnitRanges.

Another discovered benefit is the ability to forward the properties to construct another IdOffsetRange.

        _values = 5:8
        _indices = 6:9
        id = IdOffsetRange(values=_values, indices=_indices)
        @test id.values === values(id)
        @test id.values == _values
        @test id.indices === eachindex(id)
        @test id.indices == _indices
        id2 = IdOffsetRange(; id.values, id.indices)
        @test id == id2
        id3 = IdOffsetRange(; id.indices, id.values)
        @test id == id3

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.16%. Comparing base (08dc371) to head (2945d61).
⚠️ Report is 45 commits behind head on master.

Files with missing lines	Patch %	Lines
src/axes.jl	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #318      +/-   ##
==========================================
- Coverage   98.67%   95.16%   -3.52%     
==========================================
  Files           5        5              
  Lines         452      434      -18     
==========================================
- Hits          446      413      -33     
- Misses          6       21      +15     

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[jishnub]

Looking at the example from #316,

julia> Base.@kwdef struct MyIdOffsetRange
                  values::UnitRange
                  indices::UnitRange
              end
MyIdOffsetRange

julia> x = MyIdOffsetRange(values=5:8, indices=5:8)
MyIdOffsetRange(5:8, 5:8)

julia> x.values
5:8

julia> x.values === x
false

In this example, the returned results correspond exactly to the displayed ones, as both directly read the fields of the struct. However, for an IdOffsetRange, we obtain another IdOffsetRange, which isn't what was displayed.

julia> id
OffsetArrays.IdOffsetRange(values=5:8, indices=6:9)

julia> id.values
OffsetArrays.IdOffsetRange(values=5:8, indices=6:9)

julia> id.values === id
true

This isn't an objection to the PR, but I wonder if we need to be consistent here?

[mkitti]

The consistency choice I made here was for

id.values === values(id)

values is part of the API already.

If you really wanted a UnitRange, this could work:

UnitRange(id.values)

For that reason, I added it to the documentation.