[BP: release/v6 <- #230] fix: don't unescrow tokens that are moved between escrow accounts

[mergify]

When pfm is moving packets from one escrow account to another in the refund flow of a failed forward, it is erroneously calling unescrowTokens which is making the accounting in the total escrow wrong.

includes migration to fix broken escrow state (h/t @drklee3)

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This is an automatic backport of pull request #230 done by Mergify.

[mergify]

Cherry-pick of 515bdca has failed:

On branch mergify/bp/release/v6/pr-230
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Changes to be committed:
	modified:   middleware/packet-forward-middleware/e2e/packet_forward_test.go
	modified:   middleware/packet-forward-middleware/e2e/upgrade_test.go
	new file:   middleware/packet-forward-middleware/packetforward/keeper/migrator.go
	new file:   middleware/packet-forward-middleware/packetforward/migrations/v3/migrate.go
	new file:   middleware/packet-forward-middleware/packetforward/migrations/v3/migrate_test.go
	modified:   middleware/packet-forward-middleware/test/mock/bank_keeper.go
	modified:   middleware/packet-forward-middleware/test/mock/channel_keeper.go
	new file:   middleware/packet-forward-middleware/testing/previous_images/pfm_8_1_0.tar

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/workflows/packet-forward-middleware.yml
	deleted by us:   middleware/packet-forward-middleware/Dockerfile
	both modified:   middleware/packet-forward-middleware/packetforward/keeper/keeper.go
	both modified:   middleware/packet-forward-middleware/packetforward/module.go
	both modified:   middleware/packet-forward-middleware/packetforward/types/expected_keepers.go
	both modified:   middleware/packet-forward-middleware/test/mock/transfer_keeper.go
	deleted by us:   middleware/packet-forward-middleware/testing/previous_images/README.md
	deleted by us:   middleware/packet-forward-middleware/testing/simapp/app.go
	deleted by us:   middleware/packet-forward-middleware/testing/simapp/upgrades/upgrades.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally