[DONT BACKPORT][BUGFIX lts] Ensure hash objects correctly entangle as dependencies v2

[pzuraq]

This is an alternative to #19583

The previous bugfixes to {{hash}} caused a change to the semantics of
computed properties that depend on a hash. Specifically, because
{{hash}} objects are now proxies, they are constant, never updating
again after they are initially created. This is fine if you depend on
an individual key in a hash, but breaks if you depend directly on the
hash itself:

computed('hash.foo', function() {}) // this works

computed('hash', function() {}) // this will no longer rerun

This is used occasionally when you wish to depend on the dynamic keys
of a dictionary, like so:

computed('hash', function() {
  let values = [];

  for (let key in this.hash) {
    values.push(hash[key]);
  }

  return values;
})

Notably, this is not a problem with autotracking, because autotracking
will entangle the usage of these keys dynamically. So this is only a
problem with legacy systems such as computed and observer which
cannot dynamically add dependencies based on the function's runtime.

To fix this, we need to determine if a dependency is a hash when a
computed or an observer depends upon it, and then entangle all of its
keys if it is. We do this whenever the value is the last value in the
chain.

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This PR/fix ended up not working out, so we're not backporting