Typed continuations: cont.bind instructions (#6365)

This PR is part of a series that adds basic support for the [typed
continuations/wasmfx proposal](https://github.com/wasmfx/specfx).

This particular PR adds support for the `cont.bind` instruction for partially
applying continuations, documented
[here](https://github.com/wasmfx/specfx/blob/main/proposals/continuations/Overview.md#instructions).

In short, these instructions are of the form `(cont.bind $ct_before $ct_after)`
where `$ct_before` and `$ct_after` are related continuation types. They must
only differ in the number of arguments, where `$ct_before` has _n_ additional
parameters as compared to `$ct_after`, for some _n_ ≥ 0. The idea is that
`(cont.bind $ct_before $ct_after)` then takes a reference to a continuation of
type `$ct_before` as well as _n_ operands and returns a (reference to a)
continuation of type  `$ct_after`. Thus, the folded textual representation looks
like `(cont.bind $ct_before $ct_after arg1 ... argn c)`.

Support for the instruction is implemented in both the old and the new wat
parser.

Note that this PR does not implement validation of the new instruction.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/wasm2js.h b/src/wasm2js.h
index 92ba397be..5f0305877 100644
--- a/src/wasm2js.h
+++ b/src/wasm2js.h
@@ -2428,6 +2428,10 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m,
       WASM_UNREACHABLE("unimp");
     }
 
+    Ref visitContBind(ContBind* curr) {
+      unimplemented(curr);
+      WASM_UNREACHABLE("unimp");
+    }
     Ref visitContNew(ContNew* curr) {
       unimplemented(curr);
       WASM_UNREACHABLE("unimp");