MDEV-18153 Assertion `0' or Assertion `btr_validate_index(index, 0)' failed in row_upd_sec_index_entry or error code 126: Index is corrupted upon UPDATE with TIME_ROUND_FRACTIONAL

Conversion to a temporal data type resulting into a lower precision
depends on TIME_ROUND_FRACTIONAL. Taking into account this dependency in:
- indexed generated virtual column expressions
- persistent virtual column expressions

A warning is now issued if conversion from the generation expression
to the column data type depends on TIME_ROUND_FRACTIONAL.

The warning will be changed to error in 10.5