Typed continuations: cont.new instructions (#6308)

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.new` instruction for creating
continuations, documented [here(https://github.com/wasmfx/specfx/blob/main/proposals/continuations/Overview.md#instructions).

In short, these instructions are of the form `(cont.new $ct)` where `$ct` must
be a continuation type. The instruction takes a single (nullable) function
reference as its argument, which means that the folded representation of the
instruction is of the form `(cont.new $ct (foo ...))`. 

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 ae3f60e18..92ba397be 100644
--- a/src/wasm2js.h
+++ b/src/wasm2js.h
@@ -2428,6 +2428,10 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m,
       WASM_UNREACHABLE("unimp");
     }
 
+    Ref visitContNew(ContNew* curr) {
+      unimplemented(curr);
+      WASM_UNREACHABLE("unimp");
+    }
     Ref visitResume(Resume* curr) {
       unimplemented(curr);
       WASM_UNREACHABLE("unimp");