LibUnicode: Make the generated .h and .cpp paths for emoji data optional

[trflynn89]

This is to allow people making emoji to run the generator to create the expected commit message format.

For example:

# Build it:
./Meta/serenity.sh build lagom GenerateEmojiData

# Run it:
./Build/lagom/Tools/CodeGenerators/LibUnicode/GenerateEmojiData -i /tmp/emoji.txt -e ./Build/x86_64/UCD/emoji-test.txt -r ./tmp/myemoji

$ cat /tmp/emoji.txt
# group: Travel & Places

# subgroup: sky & weather
❄️ - U+2744 U+FE0F Snowflake (fully-qualified)
❄ - U+2744 Snowflake (unqualified)

# group: Symbols

# subgroup: punctuation
❓ - U+2753 Red Question Mark (fully-qualified)
❔ - U+2754 White Question Mark (fully-qualified)
❕ - U+2755 White Exclamation Mark (fully-qualified)

# subgroup: other-symbol
❌ - U+274C Cross Mark (fully-qualified)

CC @Xexxa