Fix/be respectful of special characters like exclamation marks in highlight phrases since they are also word boundaries (#1890)

* Add missing includes

We would normally have these included in another file already, or even
the precompiled headers, but having the files included here too makes
testing single parts easier.

* Modify the regex building of highlight phrases for non-regex phrases

For phrases like !test, the word boundary checking we did before was not
enough, so we now check for either a word boundary, a whitespace
character, or the line start/end.

* Add tests for ensuring I haven't fully broken the highlight system

* Add changelog entry

src/controllers/highlights/HighlightPhrase.hpp

@@ -4,10 +4,14 @@
 #include "util/RapidJsonSerializeQString.hpp"
 #include "util/RapidjsonHelpers.hpp"
 
+#include <QColor>
 #include <QRegularExpression>
 #include <QString>
+#include <QUrl>
 #include <pajlada/serialize.hpp>
 
+#include <memory>
+
 namespace chatterino {
 
 class HighlightPhrase