LibJS: Inline Cell::Visitor::visit() functions

This allows the calls to MarkingVisitor::visit_impl() during GC to be
devirtualized in Heap::mark_live_cells().

Userland/Libraries/LibJS/CMakeLists.txt

@@ -2,7 +2,6 @@ set(SOURCES
     AST.cpp
     Console.cpp
     Heap/Allocator.cpp
-    Heap/Cell.cpp
     Heap/Handle.cpp
     Heap/HeapBlock.cpp
     Heap/Heap.cpp

Userland/Libraries/LibJS/Heap/Cell.cpp

@@ -1,26 +0,0 @@
-/*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#include <LibJS/Heap/Cell.h>
-#include <LibJS/Heap/Heap.h>
-#include <LibJS/Heap/HeapBlock.h>
-#include <LibJS/Runtime/Value.h>
-
-namespace JS {
-
-void Cell::Visitor::visit(Cell* cell)
-{
-    if (cell)
-        visit_impl(cell);
-}
-
-void Cell::Visitor::visit(Value value)
-{
-    if (value.is_cell())
-        visit_impl(value.as_cell());
-}
-
-}

Userland/Libraries/LibJS/Heap/Cell.h

@@ -33,7 +33,11 @@ public:
 
     class Visitor {
     public:
-        void visit(Cell*);
+        void visit(Cell* cell)
+        {
+            if (cell)
+                visit_impl(cell);
+        }
         void visit(Value);
 
     protected:

Userland/Libraries/LibJS/Runtime/Value.h

@@ -327,6 +327,12 @@ inline Value js_negative_infinity()
     return Value(-INFINITY);
 }
 
+inline void Cell::Visitor::visit(Value value)
+{
+    if (value.is_cell())
+        visit_impl(value.as_cell());
+}
+
 Value greater_than(GlobalObject&, Value lhs, Value rhs);
 Value greater_than_equals(GlobalObject&, Value lhs, Value rhs);
 Value less_than(GlobalObject&, Value lhs, Value rhs);