Add per-document library info

[elfenlaid]

The changes introduce per-document libraries to the document model.

The gist of the changes is that now documents would have a more tangible "references" to libraries from which symbols come from. Mind that it's not libraries direct copies. Rather, it's just enough info to possibly restore libraries setup in another Sketch application. This simplifies communication between a document's authors and a document's consumers. Now consumers would know what libraries they need to install in order to work with a document

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 2d515aaa5791ee354b434d8c33005b257a0ae7cb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@sketch-hq/sketch-file-format	Minor
@sketch-hq/sketch-file-format-ts	Minor
@sketch-hq/sketch-file	Patch

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