Isolate demos folder

[LucDeCaf]

Currently, the demos in the demos folder use pnpm's workspace feature to link to workspace packages. This is convenient for testing changes to workspace packages, as demos will automatically use the local version - however, it causes issues for other users of the demos, as they are required to install all demos and all packages' dependencies in order to run even a single demo. Also, copying demos out of the monorepo requires one to figure out the correct package versions manually.

This PR replaces the @powersync/* package versions from workspace:* to the latest published releases and adds a pnpm-workspace.yaml file to each demo. This isolates the demos from the rest of the workspace and ensures that each demo can run independently from the powersync-js repo's context. For convenience, this PR also adds a set of scripts for re-linking the @powersync/* packages to the workspace (for ease of development and testing) and for upgrading @powersync/* package versions across demos.

Importantly, this PR also includes a partial rewrite of the react-native-supabase-group-chat demo, which was using old packages and failing to build on my system. The PR which made these changes was merged into this branch, since it also used published PowerSync package versions instead of workspace versions.

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Latest commit: 21fbf58

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[simolus3]

Can we add demo lockfiles to .gitignore? I imagine they make up the bulk of this PR, and I'm not sure they're that helpful (we should definitely keep the root lockfile to ensure we're all using the same version of tools).

[Chriztiaan]

Last bit of reverting version drops, then it can go in.

[LucDeCaf]

Yep, fixed the misversioned packages

[Chriztiaan]

Happy with the changes.