Add API to statically assert signature of a Func (#955)

* Add API to statically assert signature of a `Func`

This commit add a family of APIs to `Func` named `getN` where `N` is the
number of arguments. Each function will attempt to statically assert the
signature of a `Func` and, if matching, returns a corresponding closure
which can be used to invoke the underlying function.

The purpose of this commit is to add a highly optimized way to enter a
wasm module, performing type checks up front and avoiding all the costs
of boxing and unboxing arguments within a `Val`. In general this should
be much more optimized than the previous `call` API for entering a wasm
module, if the signature is statically known.

* rustfmt

* Remove stray debugging

crates/runtime/src/lib.rs

@@ -44,7 +44,7 @@ pub use crate::mmap::Mmap;
 pub use crate::sig_registry::SignatureRegistry;
 pub use crate::trap_registry::{TrapDescription, TrapRegistration, TrapRegistry};
 pub use crate::traphandlers::resume_panic;
-pub use crate::traphandlers::{raise_user_trap, wasmtime_call, wasmtime_call_trampoline, Trap};
+pub use crate::traphandlers::{catch_traps, raise_user_trap, wasmtime_call_trampoline, Trap};
 pub use crate::vmcontext::{
     VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport, VMGlobalDefinition,
     VMGlobalImport, VMInvokeArgument, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex,