Migrate internal storage of trace string to array of trace info

[colin-axner]

Summary

Migrate internal trace information of ics20 token to store individual trace hop pairs, []string, to match ics20-v2 updates

Problem Definition

In maintaining backwards compatibility, there's an unnecessary amount of parsing, joining occurring which would be largely simplified by performing this migration.

Upon SendPacket:

1. ibc token lookup occurs from hash to trace info
2. full joined path is returned
3. the full path is then re-parsed (despite its denom, path being cached)
4. in this re-parsing, we parse out the denom trace (despite it being available in step 1)
5. and then we reparse the path again (second time in this stack trace) to format the []trace pair which is set in the packet, but not internal state

In the expected flow:

1. ibc token lookup occurs from hash, returns ibc token info (denom, []trace)
2. any usage which needs full denom path (v1 compat) can do a basic strings.join on []trace

Use cases

Mostly simplifies maintenance and optimizes the code. In the long run, it would remove the possibility for a minor issue (once support for ics20-v1 is dropped)

Proposal

Perform an in-place migration which migrates the stored denom trace info from being a single string to an array of trace info. This makes internal storage compatible with the v2 approach rather than trying to reconstruct the v2 info based on v1 storage. Not essential, but likely worth the effort.

In practice we could remove/replace the DenomTrace type, ideally with a better named type

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