[paragraph] Allow multiple unicode implementations

Allow both client and non-client unicode implementations to be used at
runtime. Remove the assert when the client implmentation is present and
replace it with a sensible runtime test.

Change-Id: Ia54c719e7554c9e218a92179b691f548970c2e3d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/752457
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
1 file changed