feat: add watchOS support (tentative)

[zifeo]

Notes from Simon: I've ensured that all our tests for the Kotlin and Swift SDKs pass when they're built against this framework on watchOS simulators. I don't have an actual watchOS device to test this on, but since the link mode is the same on those platforms I think it should work. My stance is that this is good enough to merge, but we'll have to do more testing on actual devices before even announcing this as experimental.

To test this, see:

• The integration into the Kotlin SDK: watchOS support powersync-kotlin#201
• The integration into the Swift SDK: watchOS support powersync-swift#50

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Not a watchOS expert, so carefully review and guidance required.

[simolus3]

Thank you for getting started on this!

I've started looking into support for this for our Kotlin SDK here: https://github.com/powersync-ja/powersync-kotlin/tree/watchOS

[simolus3]

I've tested this against the Kotlin and Swift SDKs, so this looks good to me.

[rkistner]

@simolus3 I'm happy with the changes, but there are still some build failures

[simolus3]

Thanks, should be fixed now 👍