refactor: size improvements

* refactor: updated supported browsers

to get smaller bundlesize

* refactor: switch to private fields and methods

* refactor: remove getAbortController function

because with our new browserslist, we'll always have an AbortController

* refactor: make updateResult private

* this didn't work

returning the object and inlining the call yields "cannot redefine signal" ...

* refactor: remove/move/inline some code

* tests: focusManager

fix focusManager tests by not accessing private methods

* tests: mutationCache

remove a test that tests an impossible case

* refactor: mutationObserver

as the test said, there is no way to trigger #notify without listeners, so we can remove the whole test + code that relates to it

* refactor: mutation.setState

as the tests says, it's unused, so we can remove it completely

* test(mutations): rewrite test to not rely on internals

we can add the same observer twice and check that the observerAdded event has only been fired once

* tests: onlineManager

fix onlineManager tests by not accessing private methods

* tests: remove test for a case that cannot happen

* refactor(core): make initialState and revertState private

they have not been accessed outside of query

* tests: rewrite query tests to not depend on internals

* tests: rewrite queryCache tests to not depend on internals

* refactor: notifyOptions.cache

it was always set to true - there is no way to _not_ notify the cache

* chore: remove unused imports

* refactor: unify partialMatchKey and partialDeepEqual

* refactor: remove Array check when checking for keys during filtering

a simple truthy check suffices, as we can only pass an Array or undefined in here

* refactor: rename hashQueryKey to hashKey

because we also use it for mutationKeys

* tests: remove unnecessary condition

signal is now always defined

* tests: get rid of annoying false-positive console.error log

* tests: don't rely on internals

re-wrote some tests and removed some others that weren't easily testable without relying on internals

* docs: document size improvements

* tests: fix copyButton test

* test(vue-query): fix tests accessing private props

* resolve merge conflict

Co-authored-by: Damian Osipiuk <osipiukd+git@gmail.com>