apacheGH-43956: [Format] Allow Decimal32/Decimal64 in format (apache#…

…43976)

Widening the Decimal128/256 type to allow for bitwidths of 32 and 64
allows for more interoperability with other libraries and utilities
which already support these types. This provides even more opportunities
for zero-copy interactions between things such as libcudf and various
databases.

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Updating the documentation in Schema.fbs to explicitly state that 32-bit
and 64-bit is now allowed for bitwidths of Decimal types. This is the
only area in the the spec that mentions the allowed decimal bitwidths.
* GitHub Issue: apache#43956

---------

Co-authored-by: Antoine Pitrou <[email protected]>

docs/source/format/Versioning.rst

@@ -105,3 +105,8 @@ Version 1.4
 * Added :ref:`listview-layout` and the associated ListView and LargeListView
   types.
 * Added :ref:`variadic-buffers`.
+
+Version 1.5
+-----------
+
+* Expanded Decimal type bit widths to allow 32-bit and 64-bit types.

format/Schema.fbs

@@ -24,7 +24,7 @@
 /// Version 1.3 - Add Run-End Encoded.
 /// Version 1.4 - Add BinaryView, Utf8View, variadicBufferCounts, ListView, and
 /// LargeListView.
-/// Version 1.5 - Add Decimal32 and Decimal64
+/// Version 1.5 - Add 32-bit and 64-bit as allowed bit widths for Decimal
 
 namespace org.apache.arrow.flatbuf;