Support same set of assertion for rules using common assertions

Currently, every rule defines their own code to detect assertions, we should consider putting in common this code in `UnitTestUtils` to bring every rule at the same level when possible (detecting the same set of assertions).

This results in the following improvements:

• New support of AssertJ for:
  • S2186 (fix SONARJAVA-3352)
  • S3658
• New support of AssertJ, JUnit 3 and Fest-assert for:
  • S5776
  • S5777
  • S5778
  • S5779
  • S5783

Note that other rules also need to detect assertions, but have specific needs preventing to put anything in common:

• S2699: requires heuristics to not behave poorly
• S2970
• S3415
• S2698: ticket to add support for AssertJ (SONARJAVA-3349)
• S2701: ticket to add support for AssertJ (TODO)