variable assignment spanning multiple lines

Hello,

Indenting is missed on multi-line variable assignment, eg. for something like this I would expect the second and third line to indent:

```
$sql = "select something "
. "from somewhere "
. "where conditions=match";
```

Is there a way to configure that to happen?

Thanks...

Look at the Vim indent script for PHP, likely in the repository's main indent file. The issue is about multi-line string concatenation with the dot operator. Test the current behavior with the provided example, then examine the indentation rules for line continuations. Check if there's a configuration option or if a rule needs to be added. Verify by editing the script and testing in Vim.

Written by the indexing model from the issue text.