LibJS: Remove "uprooting" mechanism from garbage collector

The Heap::uproot_cell() API was used to implement markAsGarbage() which
was used in 3 tests to forcibly destroy a value, even if it had
references on the stack or elsewhere.

This patch rewrites the 3 tests that used this mechanism to be
structured in a way that allows garbage collection to collect the values
as intended without hacks. And now that the uprooting mechanism is no
longer needed, it's uprooted as well.

This fixes 3 test-js tests in bytecode mode. :^)

Userland/Libraries/LibJS/Tests/builtins/FinalizationRegistry/FinalizationRegistry.prototype.cleanupSome.js

@@ -3,9 +3,7 @@ test("length is 0", () => {
 });
 
 function registerInDifferentScope(registry) {
-    const target = {};
-    registry.register(target, {});
-    return target;
+    registry.register({}, {});
 }
 
 test("basic functionality", () => {
@@ -20,8 +18,7 @@ test("basic functionality", () => {
 
     expect(count).toBe(0);
 
-    const target = registerInDifferentScope(registry);
-    markAsGarbage("target");
+    registerInDifferentScope(registry);
     gc();
 
     registry.cleanupSome(increment);

Userland/Libraries/LibJS/Tests/builtins/WeakMap/WeakMap.prototype.set.js

@@ -1,3 +1,9 @@
+function registerInDifferentScope(registry) {
+    const target = {};
+    registry.register(target, {});
+    eval("");
+}
+
 test("basic functionality", () => {
     expect(WeakMap.prototype.set).toHaveLength(2);
 
@@ -21,25 +27,26 @@ test("invalid values", () => {
     });
 });
 
+function setObjectKey(weakMap) {
+    expect(weakMap.set({ e: 3 }, 1)).toBe(weakMap);
+}
+
+function setSymbolKey(weakMap) {
+    expect(weakMap.set(Symbol("foo"), "bar")).toBe(weakMap);
+}
+
 test("automatic removal of garbage-collected values", () => {
     const weakMap = new WeakMap();
-    const objectKey = { e: 3 };
 
-    expect(weakMap.set(objectKey, 1)).toBe(weakMap);
+    setObjectKey(weakMap);
     expect(getWeakMapSize(weakMap)).toBe(1);
 
-    markAsGarbage("objectKey");
     gc();
-
     expect(getWeakMapSize(weakMap)).toBe(0);
 
-    const symbolKey = Symbol("foo");
-
-    expect(weakMap.set(symbolKey, "bar")).toBe(weakMap);
+    setSymbolKey(weakMap);
     expect(getWeakMapSize(weakMap)).toBe(1);
 
-    markAsGarbage("symbolKey");
     gc();
-
     expect(getWeakMapSize(weakMap)).toBe(0);
 });

Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.add.js

@@ -16,25 +16,26 @@ test("invalid values", () => {
     });
 });
 
+function addObjectItem(weakSet) {
+    weakSet.add({ a: 1 });
+}
+
+function addSymbolItem(weakSet) {
+    weakSet.add(Symbol("foo"));
+}
+
 test("automatic removal of garbage-collected values", () => {
     const weakSet = new WeakSet();
-    const objectItem = { a: 1 };
 
-    expect(weakSet.add(objectItem)).toBe(weakSet);
+    addObjectItem(weakSet);
     expect(getWeakSetSize(weakSet)).toBe(1);
 
-    markAsGarbage("objectItem");
     gc();
-
     expect(getWeakSetSize(weakSet)).toBe(0);
 
-    const symbolItem = Symbol("foo");
-
-    expect(weakSet.add(symbolItem)).toBe(weakSet);
+    addSymbolItem(weakSet);
     expect(getWeakSetSize(weakSet)).toBe(1);
 
-    markAsGarbage("symbolItem");
     gc();
-
     expect(getWeakSetSize(weakSet)).toBe(0);
 });