Encapsed string loses literal string details for unions unlike concat

[kkmuffme]

https://psalm.dev/r/448c9d0bef

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/448c9d0bef

<?php

/**
 * @var 'hello'|'world' $a
 * @var 'foo'|'bar' $b
 * @var 'x'|'y' $c
 */

$x = $a . $b . $c;
/** @psalm-trace $x */;

$y = "hello {$a} world";
/** @psalm-trace $y */;

$z = "{$a}{$b}{$c}";
/** @psalm-trace $z */;

Psalm output (using commit 08afc45):

INFO: Trace - 10:23 - $x: 'hellobarx'|'hellobary'|'hellofoox'|'hellofooy'|'worldbarx'|'worldbary'|'worldfoox'|'worldfooy'

INFO: Trace - 13:23 - $y: non-empty-literal-string

INFO: Trace - 16:23 - $z: non-empty-literal-string

INFO: UnusedVariable - 9:1 - $x is never referenced or the value is not used

INFO: UnusedVariable - 12:1 - $y is never referenced or the value is not used

INFO: UnusedVariable - 15:1 - $z is never referenced or the value is not used