Add SVN Checker tool

[ernilambar]

This issue proposes adding an SVN Checker tool to Plugin Check that inspects a plugin's published SVN repository directly and reports inconsistencies.

• Ref: https://developer.wordpress.org/plugins/wordpress-org/how-to-use-subversion/

Features

• Add a tool that audits a WordPress.org-hosted plugin's SVN repository structure.
• Verify that trunk, tags, and assets folders exist and match what the plugin declares in its readme and plugin header.
• Detect mismatches between trunk and the tagged stable release, such as version number or stable tag differences.