Custom search path SHOULD start with a slash

Problem/Motivation

Starting internal URLs with a slash is a standard in Drupal 8+
So instead of triggering an error, IF it STARTS with a slash, it should be required to start with a slash.

Existing installations will need an update hook to prepend the / to existing values.

To validate the entered path, we could use:
$destination = Url::fromUserInput($path);
if ($destination->isRouted()) {
// Valid internal path.
}
but will have to do some cleanup before like removing the @keys variable.
We should discuss all possible cases, like URL parameters ?&=@keys also

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes