Migration to JUnit 5 - avoid using AbstractMojoTestCase

[slawekjaranowski]

also:

• refactor PropertyUtilsTest - it is not Mojo test, move use cases from advanced amd enhanced examples

• CopyResourcesMojoTest - test copy-resources instead of resources goal, add more tests for filtered and not filtered resources

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@slawekjaranowski Please assign appropriate label to PR according to the type of change.