Fix #7619. 0x prefix must be added when assigning hexadecimal string into bit column in Postgresql, because solving ambiguity.

According to https://github.com/rails/rails/blob/232d2223ebcfe5c9e0425c821f5d30a7d5968512/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb#L49 , hexadecimal data which has '0' and '1' character interpreted as binary data into bit column in PostgreSQL.

I try to fix this issue by behavior changing.

without this PR:
  "FF" # hex
  "1F" # hex
  "10" # binary !

with this PR:
  "FF" # invalid
  "0xFF" # hex
  "10" # binary

Please see #7619