Fix tag import parsing in WasmOffsetConverter (#18691)

To parse a `tag_type`, we need to skip an `uint8` for an `attribute`
and a `varuint32` for a `type`:
https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md#tag_type

Currently we only skip a byte, which I'm not sure was intended for the
attribute or the type index.

Author: aheejin

src/wasm_offset_converter.js

@@ -88,7 +88,7 @@ function WasmOffsetConverter(wasmBytes, wasmModule) {
               unsignedLEB128(); // skip function type
               break;
             case 1: // table import
-              ++offset; // FIXME: should be SLEB128
+              unsignedLEB128(); // skip elem type
               skipLimits();
               break;
             case 2: // memory import
@@ -98,7 +98,8 @@ function WasmOffsetConverter(wasmBytes, wasmModule) {
               offset += 2; // skip type id byte and mutability byte
               break;
             case 4: // tag import
-              ++offset; // // FIXME: should be SLEB128
+              ++offset; // skip attribute
+              unsignedLEB128(); // skip tag type
               break;
 #if ASSERTIONS
             default: throw 'bad import kind: ' + kind;