[FIX] Slugify emoji aliases after splitting them

[RavuAlHemio]

This allows to set multiple emoji aliases again. Otherwise the comma or space would have been replaced by an underscore before the splitting occurs.

Proposed changes (including videos or screenshots)

Split multiple emoji aliases on spaces or commas before slugifying them

Issue(s)

#18264

Steps to test or reproduce

Attempt to add an emoji with aliases specified as test1 test2 or test1,test2. The aliases are currently converted into a single alias test1_test2; after this fix, they are correctly split up into the aliases test1 and test2.

Further comments