Incorrect routing caused by str_replace in Uri::init()

[hundblue]

There are still (even after fixing #1892) occurences of incorrect use of str_replace in Uri::init(). In particular:
$uri = str_replace(static::filterPath($this->root), '', $this->url);
Instead of removing just the prefix, each occurence of the string being searched for is removed. This results in undesired route aliasing. Example:
https://learn.getgrav.org/16/content/rouhttps://learn.getgrav.orgting
is presently an alias of
https://learn.getgrav.org/16/content/routing.

Another not yet solved case of incorrect route aliasing is that of a fake hostname:
https://learn.getgrav.org/16//FAKE_HOSTNAME/content/routing (issue #2184)