GH-37653: [MATLAB] Add arrow.array.StructArray MATLAB class

[sgilmore10]

Rationale for this change

Now that many of the commonly-used "primitive" array types have been added to the MATLAB Inferface, we can implement arrow.array.StructArray class.

What changes are included in this PR?

Added arrow.array.StructArray MATLAB class.

Methods of arrow.array.StructArray include:

• fromArrays(arrays, nvpairs)
• field(i) -> get the i field as an arrow.array.Array. i can be a positive integer or a field name.
• toMATLAB() -> convert to a MATLAB table
• table() -> convert to a MATLAB table

Properties of arrow.array.StructArray include:

• Type
• Length
• NumFields
• FieldNames
• Valid

Example Usage

>> a = arrow.array([1, 2, 3, 4]);
>> b = arrow.array(["A", "B", "C", "D"]);
>> s = arrow.array.StructArray.fromArrays(a, b, FieldNames=["A", "B"])
s = 

-- is_valid: all not null
-- child 0 type: double
  [
    1,
    2,
    3,
    4
  ]
-- child 1 type: string
  [
    "A",
    "B",
    "C",
    "D"
  ]

% Convert StructArray to a MATLAB table
>> t = toMATLAB(s)

t =

  4×2 table

    A     B 
    _    ___

    1    "A"
    2    "B"
    3    "C"
    4    "D"

Are these changes tested?

Yes. Added a new test class tStructArray.m

Are there any user-facing changes?

Yes. Users can now construct an arrow.array.StructArray instance.

Notes

1. Although struct is a MATLAB datatype, StructArray's toMATLAB method returns a MATLAB table. We went with this design because the layout of MATLAB tables more closely resembles StructArrays. MATLAB tables ensure a consistent schema and the data is laid out in a columnar format. In a future PR, we plan on adding a struct method to StructArray, which will return a MATLAB struct array.
2. I removed the virtual toMATLAB method from proxy::Array because the nested array MATLAB will implement their toMATLAB method by invoking the toMATLAB method on their field arrays. There's no need for the C++ proxy classes of nested arrays to have a toMATLAB method.

Future Directions

1. Add a fromMATLAB static method to create StructArrays from MATLAB tables and MATLAB struct arrays.
2. Add a fromTable static method to create StructArrays from arrow.tabular.Tables
3. Add a fromRecordBatch static method to create StructArrays from arrow.tabular.RecordBatchs

• Closes: [MATLAB] Add arrow.array.StructArray MATLAB class #37653

[kevingurney]

Thanks for the PR! It's really nice to see nested type support being added.

[kevingurney]

+1

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 5 benchmarking runs that have been run so far on merge-commit 7b30ba4.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about possible false positives for unstable benchmarks that are known to sometimes produce them.