Add Spin-version-specific worlds to `src/spin_sdk/wit/spin.wit`

[dicej]

Currently, there's no obvious way to use the latest SDK to target older (e.g. pre-3.4) versions of Spin; the only option is to use an earlier SDK version. One easy way to address that would be to add version-specific worlds to spin.wit, e.g. one for Spin 3.2.x, one for Spin 3.3.x, etc. This will allow the user to specify which Spin version they wish to target using the --world option to componentize-py in the build directive of their spin.toml file. The default would remain the latest version of Spin supported by the SDK.

[tschneidereit]

Would it in principle be possible to have this wit file be provided by Spin dynamically? I'm asking because that's something I'd ultimately like to get to with the target environments work: have Spin not just validate finished components against a target environment's world, but provide that world as input into the build process.

[tschneidereit]

Oh, and the way I'd see this working is to have a well-known place where Spin would put a wit file before calling the component's build instructions.

[dicej]

Would it in principle be possible to have this wit file be provided by Spin dynamically?

Yes!

[tschneidereit]

Excellent! @itowlson and I just talked about this a bunch, and I think we have a pretty clear path towards doing just this.

I also think that path will take a little bit longer to walk to its end, so don't necessarily wait for that to happen before resolving this issue here, depending on urgency.