Use a transaction PoDatabaseWriter to improve performance

Profiling results running time vendor/bin/drush si -y -v standard --account-mail=alex@example.com --account-name=admin --account-pass=PASSWORD --db-url=mysql://USER:PASSWORD@localhost/DB_NAME --locale=de

With MR

________________________________________________________
Executed in    7.29 secs    fish           external
   usr time    3.14 secs    0.21 millis    3.14 secs
   sys time    0.94 secs    3.19 millis    0.94 secs

Without MR

________________________________________________________
Executed in    9.45 secs    fish           external
   usr time    3.32 secs    0.25 millis    3.32 secs
   sys time    0.93 secs    2.56 millis    0.93 secs

The results are pretty consistent and will benefit sites with more translation files to import.

alexpott → changed the visibility of the branch 3520750-use-a-transaction to hidden.