Set DICTIONARY_ORDERED flag for FFI_ArrowSchema

[viirya]

Which issue does this PR close?

Closes #2049.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #2050 (af72eeb) into master (742a590) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2050   +/-   ##
=======================================
  Coverage   83.55%   83.56%           
=======================================
  Files         222      222           
  Lines       58216    58226   +10     
=======================================
+ Hits        48645    48656   +11     
+ Misses       9571     9570    -1     

Impacted Files	Coverage Δ
arrow/src/datatypes/ffi.rs	76.56% <100.00%> (+1.56%)	⬆️
arrow/src/ffi.rs	87.52% <100.00%> (+0.04%)	⬆️
...row/src/array/builder/string_dictionary_builder.rs	90.64% <0.00%> (-0.72%)	⬇️
parquet/src/encodings/encoding.rs	93.43% <0.00%> (-0.20%)	⬇️
parquet_derive/src/parquet_field.rs	65.98% <0.00%> (+0.22%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 742a590...af72eeb. Read the comment docs.

[viirya]

Thanks @tustvold