Get rid of the dedicated Emoji class to make it easier to store a null
value signifying a failed lookup.
This allows us to remember failed lookups, making subsequent failures
for the same codepoint much faster. :^)
This was a workaround to be able to build on case-insensitive file
systems where it might get confused about <string.h> vs <String.h>.
Let's just not support building that way, so String.h can have an
objectively nicer name. :^)
This class can locate and load emojis, which are expected to be stored
as regular PNG images at /res/emoji/U+XXXX.png, where XXXX is the
character codepoint.
https://github.com/SerenityOS/serenity/issues/490
