Consider adding more type-checking to `wasm-tools component link`

Inspired by [this comment](https://github.com/bytecodealliance/wasm-tools/pull/2590#discussion_r3730085482) currently the linking phase of `wasm-tools component link` does type-checks at the item level (e.g. if something is a function or global) and type-checks for globals/tables/memories, but fine-grained type-checks of functions is not yet done. For example if functions are imported with the wrong signature that'll show up as a validation error at the end instead of a linking error. Ideally the linking phase itself would perform these sorts of type-checks and provide an error "faster" to avoid delaying it to a confusing time later on.

Start at the linking phase behind `wasm-tools component link` and trace how imported functions are currently checked versus how final validation reports signature errors. Add fine-grained function type checks so mismatches are reported during linking, then run the existing component-linking and validation tests to confirm the error occurs at the earlier stage.

Written by the indexing model from the issue text.