Make imported functions inexact

[kripken]

Defined functions remain exact, but imported ones are inexact.

This is a step along the recent Custom Descriptors spec changes.

• New RefFunc::finalize and Literal::makeFunc variants get the module, and look up
  the type there.
• New Builder::makeRefFunc variant gets a Type and applies it. The HeapType
  variant does a lookup on the module (so the Type one is more efficient/applicable
  if the IR is not fully built yet).
• ReFinalize now updates RefFunc types (following the pattern of a few other places).
• C and JS APIs now assume RefFuncs are created after imported functions (so we can
  look up the type of the import; see changelog, this seems the least-annoying way to
  update here, avoiding new APIs, and less breakage for users - hopefully none, all our
  tests here pass as is).
• wasm-split adds a cast when a function becomes an inexact import.
• Fix GUFA to handle inexact function literals.
• Update types in passes and fuzzer as needed.

[tlively]

Adding validation that defined (i.e. non-imported) functions must have exact types exposes a bug in the JSPI pass.

[kripken]

After merging main, which includes the GUFA change for imported functions, a fix was required here in GUFA.cpp:

https://github.com/WebAssembly/binaryen/pull/7993/files#diff-45bc50500f96fb0a98cf7229b7ccbe2c1a627b195a6bb2f317d979fb0cee6286

We used to only have globals as an exception there, and now must have functions as well (for imported ones). This becomes an issue in this PR as exactness changes make it noticeable, and this affected a new test here.

[kripken]

@tlively

Adding validation that defined (i.e. non-imported) functions must have exact types exposes a bug in the JSPI pass.

Where can I see that?

[tlively]

I found that when I started working on a new PR using this one as the base. Here's the diff to apply:

diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index b7487a9d1..f93da3aaf 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -4175,6 +4175,9 @@ void FunctionValidator::visitFunction(Function* curr) {
   }

   if (curr->body) {
+    shouldBeTrue(curr->type.isExact(),
+                 curr->name,
+                 "defined function should have exact type");
     if (curr->getResults().isTuple()) {
       shouldBeTrue(getModule()->features.hasMultivalue(),
                    curr->body,

[tlively]

Basically we should move the exactness type checking from visitRefFunc to visitFunction.

[kripken]

Done.

[tlively]

LGTM once CI and fuzzers are happy

[kripken]

good catch @tlively on that missing validation 😄 that caused a lot of things to be missed earlier...