feat: add Owner.root shallow property that stores the root owner

The root property can be used to store referentially unique object accessible in the owner tree. This property is copied to child owners and computations.

packages/solid/src/reactive/signal.ts

@@ -82,6 +82,7 @@ export interface SignalState<T> extends SourceMapValue {
 }
 
 export interface Owner {
+  root?: Owner;
   owned: Computation<any>[] | null;
   cleanups: (() => void)[] | null;
   owner: Owner | null;
@@ -145,6 +146,7 @@ export function createRoot<T>(fn: RootFunction<T>, detachedOwner?: typeof Owner)
         ? { owned: null, cleanups: null, context: null, owner: null }
         : UNOWNED
       : {
+          root: detachedOwner?.root ?? owner?.root,
           owned: null,
           cleanups: null,
           context: null,
@@ -1396,6 +1398,7 @@ function createComputation<Next, Init = unknown>(
     sourceSlots: null,
     cleanups: null,
     value: init,
+    root: Owner?.root,
     owner: Owner,
     context: null,
     pure