Guard imperative DOM operations (removeChild, RAF callbacks) against
race conditions where React has already unmounted the target nodes.
- assets/common.cljs: add dom/child? guard before removeChild in RAF
- dynamic_modifiers.cljs: capture RAF IDs and cancel them on cleanup;
add null guards for DOM nodes that may no longer exist
- hooks.cljs: guard portal container removal with dom/child? check
- errors.cljs: extract is-ignorable-exception? to a top-level defn
and add NotFoundError/removeChild to ignorable exceptions, since
these are caused by browser extensions modifying React-managed DOM
- Add unit tests for is-ignorable-exception? predicate
Signed-off-by: Andrey Antukh <niwi@niwi.nz>
