The UTF8MB3 character set is deprecated in 8.0

Migrate performance_schema tables to UTF8MB4.

In particular:
- change UTF8 (meaning UTF8MB3) character set to UTF8MB4
- change utf8_bin collations to utf8mb4_bin
- change utf8_general_ci collation to the default (utf8_0900_ai_ci)

Adjust all test cases accordingly.