[core] Add a filter possibility to FileCollector

[adangel]

Describe the PR

This adds a new API method in FileCollector in order to filter files before they are added.
Needed to fix #4942. The logic is the same as in PMD 6, meaning: if the filename (not the path) is the same and the file size, then the file is considered a duplicate.

We could do a checksum comparison or something like that, but this would then a behavioral change or a new feature.

Related issues

• Fixes [core] CPD: --skip-duplicate-files has no effect (7.0.0 regression) #4942

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by github actions)
• Added (in-code) documentation (if needed)

[pmd-test]

	1 Message
📖	Compared to master: This changeset changes 0 violations, introduces 141 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Download full report as build artifact
✅	Compared to master: This changeset changes 0 violations, introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Download full report as build artifact

Generated by 🚫 Danger