Handle variadic and not declared arguments in stack traces

[xwillq]

This pull request fixes #1645. Short summary: SDK wasn't sending some function arguments to Sentry, namely default, variadic, not declared arguments and arguments with value null. This pull request reworks function responsible for handling parameters in order to send all of the above.

I tested my changes with all inputs variations I could think of, it seems to be working. However, I don't quite understand how to add tests for it. Testing this method requires using stack trace with real function or real class and method. Where do I create them? Current FrameBuilder tests don't do anything similar, so I'm not sure what would be the right way to do it.

Also, PHPStan gives me Unreachable statement - code above always terminates. error on lines 254 and 267. Those statements are definitely reachable, and I confirmed it with manual testing. I tried changing method parameter from mixed[] to array<array-key, mixed> but it didn't help. Do you have an idea what could be causing this?