fix($location): correctly handle external URL change during `$digest`

Previously, when the URL was changed directly (e.g. via `location.href`) during
a `$digest` (e.g. via `scope.$evalAsync()` or `promise.then()`) the change was
not handled correctly, unless a `popstate` or `hashchange` event was fired
synchronously.

This was an issue when calling `history.pushState()/replaceState()` in all
browsers, since these methods do not emit any event. This was also an issue when
setting `location.href` in IE11, where (unlike other browsers) no `popstate`
event is fired at all for hash-only changes ([known bug][1]) and the
`hashchange` event is fired asynchronously (which is too late).

This commit fixes both usecases by:

1. Keeping track of `$location` setter methods being called and only processing
   a URL change if it originated from such a call. If there is a URL difference
   but no setter method has been called, this means that the browser URL/history
   has been updated directly and the change hasn't yet been propagated to
   `$location` (e.g. due to no event being fired synchronously or at all).
2. Checking for URL/state changes at the end of the `$digest`, in order to
   detect changes via `history` methods (that took place during the `$digest`).

[1]: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/3740423/

Fixes #11075
Fixes #12571
Fixes #15556

Closes #15561