Refactor indices pallet to use fungible traits #44814

Job	Run time
isdraft / isdraft	3s
preflight / preflight	49s
preflight / ci-versions	1m 11s
check-runtime-migration (bridge-hub-westend)	5m 17s
check-runtime-migration (asset-hub-westend)	22m 34s
check-runtime-migration (collectives-westend)	5m 0s
check-runtime-migration (westend)	7m 51s
check-runtime-migration (coretime-westend)	5m 42s
All runtime migrations passed	2s
	48m 29s

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