Support CAST from Decimal datatype to String

[comphead]

Which issue does this PR close?

Closes #3991.

Rationale for this change

Support cast Decimal datatype to string

What changes are included in this PR?

Are there any user-facing changes?

No

[comphead]

@tustvold not sure why the test fails on

Test casting Decimal128(38, 0) --> LargeList(Field { name: "item", data_type: Utf8, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} })
thread 'test_can_cast_types' panicked at 'called `Result::unwrap()` on an `Err` value: InvalidArgumentError("non-nullable child of type Utf8 contains nulls not present in parent LargeList(Field { name: \"item\", data_type: Utf8, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} })")', arrow-data/src/data/mod.rs:1795:30

Perhaps related to #3983

[tustvold]

My guess is the cast is failing and inserting a null, but the field doesn't permit nulls. I'm not sure what the cast kernel should do in such a case tbh, but in the immediate term I'd suggest finding a way to avoid the decimal cast from failing

[comphead]

My guess is the cast is failing and inserting a null, but the field doesn't permit nulls. I'm not sure what the cast kernel should do in such a case tbh, but in the immediate term I'd suggest finding a way to avoid the decimal cast from failing

@tustvold I have removed None from decimal array as other tests casts with not nullable values

[tustvold]

Just some minor nits

[tustvold]

I took the liberty of resolving the merge conflicts on this