GH-49071: [Ruby] Add support for writing list and large list arrays (#49072)

### Rationale for this change

They use different offset size.

### What changes are included in this PR?

* Add `ArrowFormat::ListType#to_flatbuffers`
* Add `ArrowFormat::LargeListType#to_flatbuffers`
* Add `ArrowFormat::VariableSizeListArray#child`
* Add `ArrowFormat::VariableSizeListArray#each_buffer`
* `garrow_array_get_null_bitmap()` returns `NULL` when null bitmap doesn't exist
* Add `garrow_list_array_get_value_offsets_buffer()`
* Add `garrow_large_list_array_get_value_offsets_buffer()`

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes.
* GitHub Issue: #49071

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>