[12.x] Simplify ParsesQueue@parseQueue logic

[rodrigopedra]

• PR Feature/queue pause resume #57800 introduced queue pause/resume
• PR [12.x] Clean up queue pausing #57863 cleaned up the code and moved the queue parsing logic to a common trait to be used by both queue:pause and queue:resume commands

This PR

• Tidies up the queue parsing logic within the Illuminate\Queue\Console\Concerns\ParsesQueue@parseQueue method
  • If a negative length is given to array_pad, then the array is padded to the left, and as such the queue value always ends up on the $queue variable.
  • By defaulting $connection to null, we can remove the ternary operator from the return statement and use the null coalescing operator to replace a missing value with its default value, without context swapping the $connection and $queue variables.
• Adds test cases to ensure parsing happens as expected.

I also defaulted $queue to the default queue when an empty string is given, but I can revert that if wanted.

[rodrigopedra]

Failing tests are unrelated to the changes proposed in this PR.