Add new UnwrapFinally mutator

[sidz]

This PR:

• Adds new UnwrapFinally mutator (Requested in: RFC: Unwrap finally mutator #1680)
• Covered by tests
• Doc PR: Update mutators.md with UnwrapFinally mutator site#245

Mutates:

$check = true;
- try {
-     $callback();
- }
- } finally {
-     $check = false;
- }
+ $callback();
+ $check = false

or

$check = true;
try {
    $callback();
} catch (\Throwable $e) {
    throw $e;
}
- } finally {
-     $check = false;
- }
+ $check = false

[maks-rafalko]

👌

please update the docs as well

[sidz]

Done