Switch romanize plugin to Keruald implementation

Summary:
The romanize() code has been refactored and packaged into the
Keruald OmniTools library.

It also fixes a bug for numbers greater than 1000.

Future evolution is to transfer functions from the core to this library too.

Test Plan: Unit tests provided.

Reviewers: dereckson

Differential Revision: https://code.zed.dereckson.be/D14