Correctly clear memory / table info in clearModule (WebAssembly#2536)

Currently `ModuleUtils::clearModule` does not clear `exists` flags in
the memory and table, and running RoundTrip pass on any module that has
a memory or a table fails as a result. This creates `clear` function in
`Memory` and `Table` and makes `clearModule` call them.

Author: aheejin

src/ir/module-utils.h

@@ -135,8 +135,8 @@ inline void clearModule(Module& wasm) {
   wasm.functions.clear();
   wasm.globals.clear();
   wasm.events.clear();
-  wasm.table.segments.clear();
-  wasm.memory.segments.clear();
+  wasm.table.clear();
+  wasm.memory.clear();
   wasm.start = Name();
   wasm.userSections.clear();
   wasm.debugInfoFileNames.clear();

src/wasm.h

@@ -1241,6 +1241,13 @@ class Table : public Importable {
 
   Table() { name = Name::fromInt(0); }
   bool hasMax() { return max != kUnlimitedSize; }
+  void clear() {
+    exists = false;
+    name = "";
+    initial = 0;
+    max = kMaxSize;
+    segments.clear();
+  }
 };
 
 class Memory : public Importable {
@@ -1284,6 +1291,14 @@ class Memory : public Importable {
 
   Memory() { name = Name::fromInt(0); }
   bool hasMax() { return max != kUnlimitedSize; }
+  void clear() {
+    exists = false;
+    name = "";
+    initial = 0;
+    max = kMaxSize;
+    segments.clear();
+    shared = false;
+  }
 };
 
 class Global : public Importable {

test/passes/roundtrip.txt

@@ -5,3 +5,7 @@
   (unreachable)
  )
 )
+(module
+ (memory $ 1 1)
+ (table $ 0 funcref)
+)

test/passes/roundtrip.wast

@@ -9,3 +9,8 @@
     (nop)
   )
 )
+
+(module
+ (memory 1 1)
+ (table 0 funcref)
+)