[Feature Request]: Compress (Un)BoundedSourceAsSdfWrapper element and restriction coders

What would you like to happen?

A typical BoundedSource may be split into many BoundedSource instances during initial splitting. Doing a simple test of the BigtableSource shows that encoding 10 instances after splitting took on average 102660 bytes while compressing each instance separately after encoding took 1639 bytes for a >60x improvement.

Issue Priority

Priority: 2

Issue Component

Component: sdk-java-core