Support references

[AndrolGenhald]

References aren't really supported by Psalm at the moment outside of ReferenceConstraintViolation and related issues when using references in arguments. It would be nice to fully support references.

https://3v4l.org/mQ809
https://psalm.dev/r/d79b9b2f0f

See also #7252 (when fixed skipped tests should be unskipped).

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/d79b9b2f0f

<?php

$a = 1;
$b = &$a;
$b = 2;
$c = 3;
$b = &$c;
$b = 4;

/** @psalm-trace $a, $b, $c */;

Psalm output (using commit 0ec8dd2):

INFO: Trace - 10:31 - $a: 1

INFO: Trace - 10:31 - $b: 4

INFO: Trace - 10:31 - $c: 3

[orklah]

Yeah, I believe we also have some flaws about references wrongly considered unused. I tried to flag issues related to references here: https://github.com/vimeo/psalm/issues?q=is%3Aissue+is%3Aopen+label%3Areferences