Add Expression::dump for use while debugging (#2912)

I have found that similar dump functions have been extremely helpful
while debugging LLVM. Rather than re-implement this locally whenever I
need it, it would be better have this utility upstream.

src/wasm.h

@@ -588,6 +588,9 @@ class Expression {
     assert(int(_id) == int(T::SpecificId));
     return (const T*)this;
   }
+
+  // Print the expression to stderr. Meant for use while debugging.
+  void dump();
 };
 
 const char* getExpressionName(Expression* curr);

src/wasm/wasm.cpp

@@ -16,6 +16,7 @@
 
 #include "wasm.h"
 #include "ir/branch-utils.h"
+#include "wasm-printing.h"
 #include "wasm-traversal.h"
 
 namespace wasm {
@@ -93,6 +94,13 @@ Name ATTR("attr");
 
 // Expressions
 
+void Expression::dump() {
+  WasmPrinter::printExpression(this,
+                               std::cerr,
+                               /*minify=*/false,
+                               /*full=*/true);
+}
+
 const char* getExpressionName(Expression* curr) {
   switch (curr->_id) {
     case Expression::Id::InvalidId: