[pull] main from Shopify:main - #202

…stry (#3932)

On iOS (and Android), every image drawn in a Canvas — most visibly
makeImageFromView snapshots at ~W*H*4 bytes each — could stay resident
after dispose(), GC, and unmount:

1. NativeReanimatedContainer never stopped its Reanimated mapper on
   unmount; stopMapper only ran at the start of the next redraw, which
   never comes for an unmounted Canvas. The leaked mapper closure
   permanently retained the recorder (whose commands hold sk_sp<SkImage>
   copies of every drawn image) and the SkPicture, so the CFData pixel
   copy made in ViewScreenshotService was never released. Stop the
   mapper in unmount() (native and web containers).

2. The leaked mapper (or the queued first-frame runOnUI) kept calling
   setJsiProperty(nativeId, "picture", ...) after the native view had
   unregistered, and ViewRegistry::withViewInfo recreated the erased
   entry, storing the sk_sp<SkPicture> in the process-global registry
   under a nativeId that is never reused — a permanent leak. Tombstone
   unregistered ids so late property updates get a transient info object
   instead of resurrecting the entry (registration paths revive the id,
   which also keeps ids valid across JS reloads).

3. requestRedraw/makeImageSnapshot(Async)/size created empty registry
   entries for unknown ids; they now use a read-only lookup.