Add non-standard Emoji_Test property

[mathiasbynens]

The full set of strings in https://unicode.org/Public/emoji/13.1/emoji-test.txt is useful for font providers to have, even though it’s not exposed as an official property. We should make this data easily available regardless. Perhaps under the name Emoji_Test?

[mathiasbynens]

Implemented + published in v1.0.4 of each package.

require('@unicode/unicode-13.0.0/Sequence_Property/Emoji_Test/index.js'); // array containing a string for each sequence