fix($location): always decode special chars in `$location.url(value)`

The original fix for #16312 included changing how `$location.url(value)`
decoded the special characters passed to it as a setter.
This broke a number of use cases (mostly involving the ui-router).

Further analysis appears to show that we can solve #16312, to prevent
urls being rewritten with decoded values, without modifying the
behaviour of `$location.url`.

This commit reverts changes to `$location.url(value)` so that encoded
chars will once again be decoded and passed to `$location.path(value)`.
In particular it will convert encoded forward slashes, which changes how
the path is updated, since e.g. `a/b/%2Fc%2Fd` will become `a/b/c/d`.
While this is arguably not "correct", it appears that there are too many
use cases relying upon this behaviour.