Instead of manually updating emoji.txt whenever new emoji are added,
we use Unicode's emoji-test.txt to generate emoji.txt on each build,
including only the emojis that Serenity supports at that time.
By using emoji-test.txt, we can also include all forms of each emoji
(fully-qualified, minimally-qualified, and unqualified) which can be
helpful when double-checking how certain forms are handled.
Some of the .gitignore rules of the main directory were leaking into the
Base directory, causing inconsistencies between what is ignored and what
is already checked-in.
Resolve that by explicitly unignoring all files in the Base directory
unless overwritten by a .gitignore file in a subdirectory.