[V110-specific] Add failed-refund external coins to their pools' BalanceAsset
[V110-specific]
Intended to close #1517 (closed)
'Failed-refund external-chain coins stay in the vaults yet are not returned to their pool'.
Though I note this pipeline passes,
I predict (and include as a later commit in this merge request)
that a Donate (or PoolMod?) event emission is still needed/appropriate for Midgard pool depth synchronisation
(as well as being convenient for analytics).
A MintBurn event is already emitted for failed-refund synth burning;
for consistency, my current impression is that a Reserve event should also be emitted for failed-refund RUNE.
Edited by Multipartite