InputCommon: fix serialization of control expression with line breaks

The control expression editor allows line breaks, but the serialization was
losing anything after the first line break (/r /n).
Instead of opting to encode them and decode them on serialization
(which I tried but was not safe, as it would lose /n written in the string by users),
I opted to replace them with a space.

Source/Core/Common/StringUtil.h

@@ -52,6 +52,8 @@ std::string_view StripQuotes(std::string_view s);
 
 std::string ReplaceAll(std::string result, std::string_view src, std::string_view dest);
 
+void ReplaceBreaksWithSpaces(std::string& str);
+
 bool TryParse(const std::string& str, bool* output);
 
 template <typename T, std::enable_if_t<std::is_integral_v<T> || std::is_enum_v<T>>* = nullptr>