[GR-54677] Support new exception handling proposal

[graalvmbot]

The new exception handling proposal as opposed to the legacy one uses a new try_table block for exception catching, if inside that block an exception is thrown, Wasm breaks to the block specified in the try_table's catch clauses. This makes exception control-flow the same as any other break-based control-flow, but makes it a bit harder for us.

This required support for Wasm blocks that return a result, which also made the validator more complex.

The new exception handling is used by default. The legacy proposal can be re-enabled using -H:+LegacyExceptions. In node (before version 25), the new exceptions are behind the --experimental-wasm-exnref flag.

---

WithExceptionNodes are now lowered to the following (see WasmIRWalker#lowerWithException for more details):

(block $exnBlock (result $throwable)
    (try_table (catch $exc_tag $exnBlock)
        WithExceptionNode();
        br Successor
    )
)
(local.set $exc_var)
ExceptionEdge();

This is optimal in terms of number of required blocks.

This does not seem to have an effect on code size.