add icons using string format to vue3

[jasonlundien]

This PR allows us to use string format to add icons to vue3 projects.

Example: <font-awesome-icon icon="fa-duotone fa-coffee" size="5x" /> <font-awesome-icon icon="fad fa-user-secret" size="5x" />

Previously we could only add using array syntax: <font-awesome-icon :icon="['fa-duotone', 'fa-coffee']" size="5x" color="red"/> <font-awesome-icon :icon="['fad', 'coffee']" size="5x" />

Requested by this issue: #347

Dependencies: This PR is dependent upon and should be merged into vue3-add-bounce-shake-tests.