Fix memory leak hotspots

- render: alias the root Fragment's props.children to its diffed _children so in-place rerenders release replaced vnode generations instead of pinning the first render's tree (#4909, #4905)
- unmount: null vnode._children and component._globalContext so a retained unmounted vnode/component can't keep the subtree's vnode shells or the ancestor provider chain alive

Author: JoviDeCroock

src/diff/index.js

@@ -654,7 +654,10 @@ export function unmount(vnode, parentVNode, skipRemove) {
 			}
 		}
 
-		r.base = r._parentDom = NULL;
+		// Also drop the context chain: an unmounted component instance is often
+		// kept alive by user code (subscriptions, timers, devtools), and should
+		// not pin every ancestor provider through _globalContext.
+		r.base = r._parentDom = r._globalContext = NULL;
 	}
 
 	if ((r = vnode._children)) {
@@ -673,7 +676,10 @@ export function unmount(vnode, parentVNode, skipRemove) {
 		removeNode(vnode._dom);
 	}
 
-	vnode._component = vnode._parent = vnode._dom = UNDEFINED;
+	// Null _children as well: a single retained unmounted vnode (e.g. held in
+	// user code or an ancestor's props.children) should not chain the entire
+	// unmounted subtree's vnode shells.
+	vnode._component = vnode._parent = vnode._dom = vnode._children = UNDEFINED;
 }
 
 /** The `.render()` method for a PFC backing instance. */

src/render.js

@@ -66,6 +66,13 @@ export function render(vnode, parentDom, replaceNode) {
 
 	// Flush all queued effects
 	commitRoot(commitQueue, vnode, refQueue);
+
+	// Alias the root Fragment's props.children to its diffed _children. The
+	// props object is created by us above and never observable by user code.
+	// In-place rerenders (renderComponent) swap vnodes in the _children array;
+	// without this alias, props.children would pin the first render's entire
+	// vnode tree in memory for the lifetime of the root. See #4909 / #4905.
+	vnode.props.children = vnode._children;
 }
 
 /**