Implement Wasm proposal: tail-call

[Robbepop]

This is about adding support for the tail-call Wasm proposal.

The tail-call Wasm proposal has recently been moved to Phase 4 with respect to the Wasm standardization and is fairly light weight, therefore implementing it won't be a lot of work and we can expect it to be stabilized very soon. Furthermore having tail-call support in wasmi will be an enabler for self-hosting wasmi once (or if) we actually make use of tail-call based instruction dispatch.

Generally we should keep up with supporting finished Wasm proposals as this allows us to keep the Wasm spec test suite up to date.