[SUREFIRE-2037] Allow for surefire-junit-platform's TestMethodFilter to support custom TestSources

**[Krzysztof Sierszeń](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=JIRAUSER286409)** opened **[SUREFIRE-2037](https://issues.apache.org/jira/browse/SUREFIRE-2037?redirect=false)** and commented

Since JUnit 5 allows for custom `{}TestSource{`}s to be configured, `TestMethodFilter` could provide a way for those sources to be recognized and filterable. This way, custom method sources will enjoy the same filtering capabilities that method sources do. 

For now, this change specifically targets ArchUnit's `FieldSource`, and I'm planning to use the solution provided to solve [the following issue](https://github.com/TNG/ArchUnit/issues/641). 

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**Affects:** 3.0.0-M5

**Remote Links:**
- [GitHub Pull Request #487
](https://github.com/apache/maven-surefire/pull/487)
- [Related issue
](https://github.com/TNG/ArchUnit/issues/641)

Start with the surefire-junit-platform TestMethodFilter entry point and review the linked GitHub Pull Request #487. Trace how JUnit 5 TestSources are recognized and filtered, with ArchUnit's FieldSource as the stated target. Done means custom method sources receive the same filtering capabilities as standard method sources.

Written by the indexing model from the issue text.