Ref D18867
Isolate the ecash-lib changes needed for ecash-wallet chained txs in this diff. In this way, we can ensure they are published and available for ecash-wallet to pull in as a dep.
The changes to action.ts introduce optional params not yet supported in ecash-wallet. The published version of ecash-wallet will not be on this version of ecash-lib until D18867 lands, so no behavior change is expected.