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GH-37568: [MATLAB] Implement `isequal` for the `arrow.tabular.Schema` MATLAB class (#37619)



### Rationale for this change

Following on to https://github.com/apache/arrow/pull/37474, https://github.com/apache/arrow/pull/37446, and https://github.com/apache/arrow/pull/37525, we should implement `isequal` for the `arrow.tabular.Schema` MATLAB class.

### What changes are included in this PR?

1. Updated `arrow.tabular.Schema` class to inherit from `matlab.mixin.Scalar`.
2. Added `isequal` method to `arrow.tabular.Schema`.

### Are these changes tested?

Yes. Added `isequal` unit tests to `tSchema.m`

### Are there any user-facing changes?

Yes. Users can now compare two `arrow.tabular.Schema` objects via `isequal`.

**Example**
```matlab
>> schema1 = arrow.schema([arrow.field("A", arrow.uint8), arrow.field("B", arrow.uint16)]);
>> schema2 = arrow.schema([arrow.field("A", arrow.uint8), arrow.field("B", arrow.uint16)]);
>> schema3 = arrow.schema([arrow.field("A", arrow.uint8)]);

>> isequal(schema1, schema2)

ans =

  logical

   1

>> isequal(schema1, schema3)

ans =

  logical

   0
```

### Future Directions
1. #37570 

* Closes: #37568

Authored-by: Sarah Gilmore <sgilmore@mathworks.com>
Signed-off-by: Kevin Gurney <kgurney@mathworks.com>