Terminal: Add some basic emoji support

This is not as perfect as it is elsewhere in the system, as we cannot
really change how terminal "thinks about" characters and bytes. What
we can do though, and what this commit does, is to *render* emojis, but
make it seem as if they take up all the space, and all the columns their
bytes would take if they were all regular characters.

Libraries/LibVT/Terminal.h

@@ -82,6 +82,8 @@ public:
         void clear(Attribute);
         bool has_only_one_background_color() const;
         void set_length(u16);
+        StringView text() const { return { characters, m_length }; }
+
         u8* characters { nullptr };
         Attribute* attributes { nullptr };
         bool dirty { false };