[GLib] Add decimal128 array builder

[asfimport]

Support Decimal128Array and DecimalType.

Reporter: Yosuke Shiro / @shiro615
Assignee: Yosuke Shiro / @shiro615

PRs and other links:

• GitHub Pull Request #2152

_{Note: This issue was originally created as ARROW-2729. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 2152
#2152