Add APIs to decimal vector for writing big endian data

[asfimport]

We recently moved Dremio to LE Decimal format (similar to Arrow). As part of that we introduces some APIs in decimal vector which take a big endian data and swap the bytes while writing into the ArrowBuf of decimal vector.

The advantage of these APIs is that caller would not have to allocate an additional memory and write( and read) source big endian twice for swapping into new memory and using that to write into the vector.

We can directly swap bytes while writing into the vector – just read once and swap while writing.

Reporter: Siddharth Teotia / @siddharthteotia
Assignee: Siddharth Teotia / @siddharthteotia

PRs and other links:

• GitHub Pull Request #1443

_{Note: This issue was originally created as ARROW-1946. Please see the migration documentation for further details.}

[asfimport]

Siddharth Teotia / @siddharthteotia:
Issue resolved by pull request 1443
#1443