test(p2-shim): exercise instantiation generic types

[eduardomourar]

Summary

@bytecodealliance/preview2-shim/instantiation has three related typing bugs that make the documented versioned-import workflow unusable:

• WASIShimConfig, SandboxConfig, GetImportObjectArgs, WASIImportObject, and VersionedWASIImportObject were declared without export in types/instantiation.d.ts, so consumers can't name them (TS2459/TS2305).
• getImportObject's version generic lived only on a dead duplicate class declaration in types/; the implementation that's actually emitted to dist/common/instantiation.d.ts had no generic at all, so passing asVersion and a type argument together failed (TS2558).
• The ./instantiation export's types condition pointed at ./dist/common/*.d.ts, where * is a literal filename rather than a pattern — it only resolved by accidental fallback to the .js target.

Changes

• Export the five types from types/instantiation.d.ts; drop the dead duplicate WASIShim class declaration there.
• Move the generic onto the real getImportObject implementation in src/common/instantiation.ts, inferring V from asVersion instead of requiring it twice; re-export the public types so they survive into dist/.
• Fix the ./instantiation types condition to point directly at dist/common/instantiation.d.ts.
• Add a regression test (test/types.ts + test/fixtures/types/instantiation-generics/) that compiles the documented versioned-import snippet and fails with the original errors against the pre-fix code.

[vados-cosmonic]

Ah nice catch @eduardomourar thanks for submitting this, this should prevent this from happening again

Code looks good to me (outside of the fmt failure) but once you're done I'm happy to review and merge this!