set trailing slash optional in route matching

[touletan]

Description

Regexp has been updated to set trailing slash as optional in route matching.

Motivation and Context

link to issue 3024.

How Has This Been Tested?

New test has been added. The previous change to keep trailing slash when it match with rest operator is still working.
This is removing the previoous breaking change of always keeping the trailing slash.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires a documentation update, and I've opened a pull request to update it already:
• I have read https://mithril.js.org/contributing.html.