Add test vectors that use i18n strings

[msporny]

Transferring this issue from w3c/vc-data-integrity#218:

The test vectors use human-readable strings and the i18n group requested that we express them using the appropriate @language/@direction values across vc-data-integrity, vc-di-eddsa, and vc-di-ecdsa. This is a tracking issue to make sure we update the test vectors to conform to i18n guidance.