arrow

GH-35871: [Go] Account for struct validity bitmap in `array.ApproxEqual` (#35872)

### Rationale for this change

When comparing `array.Struct` values with `array.ApproxEqual` the validity bitmap of the struct itself should take precedence:
> When reading the struct array the parent validity bitmap takes priority.

This follows a brief discussion from #35851.

### What changes are included in this PR?

`array.arrayApproxEqualStruct` will check the fields data only if the struct elem is valid.

### Are these changes tested?

`pqarrow` tests are updated accordingly (no special treatment for structs, just `array.ApproxEqual`

### Are there any user-facing changes?

`array.ApproxEqual` behavior changed to match the docs about validity bitmap precedence.

* Closes: #35871

Authored-by: candiduslynx <candiduslynx@gmail.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>