Refactor/foreign assets as thin proxy #2219

Job	Run time
canary	0s
forkless-update-data	0s
try-runtime	0s
collator-selection	0s
forkless-update-no-data	0s
node-only-update	0s
governance	0s
xcm / Prepare execution matrix	27s
unit-test / develop	8m 52s
yarn-dev / opal	31m 59s
yarn-dev / sapphire	31m 51s
yarn-dev / quartz	32m 25s
yarn-dev / unique	26m 15s
codestyle / clippy	2m 38s
codestyle / rustfmt	16s
codestyle / yarn_eslint	28s
xcm / opal	1h 29m 14s
xcm / quartz	2h 55m 30s
xcm / unique	3h 8m 26s
	9h 48m 21s

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