Allow route parameters, e.g. for entity.node.canonical node IDs

Problem/Motivation

I sadly for got that we'll need (named) route parameters.

See https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Url.php/f...
We don't need options.

For example we need a node:123 parameter for entity.node.canonical route.

Tour module does it like this:

entity.node.canonical
- node:2

But I'd rather like to keep one route per line and the tour implementation also is no standard, but yml and I don't think it would be nice to change the logic here.

So here's my suggestion:
Let's split the route parameters by slash (/) and each key-value pair by ":", e.g.:

entity.node.canonical/node:123
entity.node.canonical/node:123/another_param:456

And hope there won't be any conflicts.

Code-wise we'll then have to explode by slash first and each result colon then!

Also please add a description to the field with explanation and these examples.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes