Detect access to uninitialized variables in combination with the null coalescing operator (??)

[odan]

Bug report

PHPStan cannot detect access to uninitialized variables when using the null coalescing operator (??).

There should be a difference beetween uninitialized variables and accessing an initialized variable that could contain null.

Code snippet that reproduces the problem

https://phpstan.org/r/fc07a0fb-3326-42ca-8b12-121995e8e780

Expected output

An Error like: "Undefined variable: $foo" or "An uninitialized array is being accessed".

[ondrejmirtes]

Duplicate of #1823