feat: reworks testng7 support

[Zlika]

Short description of what this resolves:

This PR is a rework of the testng7 support added in #232.
The problems with the original testng7 support are:

• It's not working (cf. arquillian-testng.jar does not include jcommander when using TestNG 7 #258).
• It creates unnecessary code duplication (3 modules are copied for a single line of code changed).
• It breaks compatibility with existing code when migrating from testng <7 to testng7 (package name changed).
• It makes people believe that the new modules can only be run using testng7 (whereas it is compatible starting from testng 6.0.1 released 9 years ago!).

Changes proposed in this pull request:

• The "new" testng7 modules are removed.
• The code now tests the existence of the ITestNGMethod.getMethod() method (testng <7) and if it does not exist call ITestNGMethod.getConstructorOrMethod() (testng>=6.0.1) instead.

This way: no more code/module duplication, and we are compatible with all versions of testng (if compatibility with testng versions older than 6.0.1 is not required, no need for reflection, just replace ITestNGMethod.getMethod() with ITestNGMethod.getConstructorOrMethod()).
I tested this PR on a project using testng7 and it works (no need for manually adding testng/jcommander as a compile dependency like the workaround proposed in #258).

Fixes #258

[Zlika]

Hello! Anyone to review this PR?

[Zlika]

Hi @bartoszmajsak ! Could you please review this PR? I really need Arquillian to be compatible with TestNG7.

[bartoszmajsak]

Hey, sure. I'll take care of it today.

[bartoszmajsak]

Many thanks for this clean-up. Much appreciated. I will cut the release today with few other PRs.