Added exports for multichain package

[shanejonas]

Explanation

Added ESM exports for multichain package

References

Changelog

@metamask/package-a

• : Your change here
• : Your change here

@metamask/package-b

• : Your change here
• : Your change here

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes