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

tests/.clang-format

@@ -0,0 +1,34 @@
+Language: Cpp
+
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+BasedOnStyle: Google
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+    BeforeElse: 'true'
+}
+BreakBeforeBraces: Custom
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+IndentPPDirectives: AfterHash
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+Standard: Auto
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