Treat starting single quote as verbatim text in Slim

[RobinMalfait]

This PR fixes an issue in Slim templates where a single quote ' at the start of the line (excluding white space) is considered a line indicator for verbatim text. It is not considered a string in this scenario.

So something like this:

div
  'Foo'

Will compile to:

<div>Foo'</div>

Fixes: #17081

[philipp-spiess]

I wonder if our pre-processor logic should also only process stuff per-line so we avoid this kind of behavior? 🤔

[RobinMalfait]

@philipp-spiess I was thinking about that as well, but it makes it potentially harder for other checks where [ and ] needs to be balanced but they might be spread across multiple lines 🤔