LibUnicode+LibWeb: Rework bidirectional_class() API a bit

[nico]

Before this commit, GenerateUnicodeData generated a
BidirectionalClass enum directly from UnicodeData.txt.

Now, GenerateUnicodeData instead generates BidirectionalClassInternal
and CharacterTypes.h has an explicit enum BidiClass with nicer names
-- no underscores, but also names more similar to ICUs names.

(Since CharacterTypes.h is included in some of LibUnicode's generators,
it can't refer to generated BidirectionalClassInternal, so we instead
have a big manual mapping switch in UnicodeData.cpp.)

bidirectional_class() used to return an Optional<BidirectionalClass>
for when unicode data was disabled. Now we return BidiClass and
just return BidiClass::LeftToRight instead of making every client
do this.

It also updates LibWeb's Element.cpp to this new system.

Also remove now-unused bidirectional_class_from_string().

This kind of cherry-picks the 4th commit of
LadybirdBrowser/ladybird#239 (aa3a30870b58c47cb37bce1418d7e6bee7af71d9):
The CharacterTypes.h, Element.cpp and TestUnicodeCharacterTypes.cpp changes are
by trflynn.

Co-authored-by: Tim Flynn trflynn89@serenityos.org

[nico]

@trflynn89 Do you want to look at LibUnicode changes over here, or should I just merge?

[trflynn89]

Code LGTM. This does break the ability to build with UCD downloads disabled - I generally tried to keep that config building/non-crashing, but if we want to step away from that, that's fine. (I don't know if the build even currently works with UCD downloads disabled, it was just something I tested every couple months or so, or if someone using the option pointed out that it broke).

[nico]

I didn't test it, but I intended that that keeps working. There's still a weak symbol of the generated function. Is there more I have to take care of?

(I suppose I could actually try building with it disabled...)

[nico]

...oh, probably because I'm using the generated enum values unconditionally. I'll tweak that, thanks!

[nico]

Done!

(I did try changing ENABLE_UNICODE_DATABASE_DOWNLOAD to OFF in Build/lagom/CMakeCache.txt and checked that Meta/serenity.sh build lagom pdf failed to build, and after the tweak it builds fine.)