Add support for MessageFormat 1

[jsahleen]

Add support for MessageFormat 1 to export and import commands. Update msg library to the latest version.

User Stories

1. As a msg-cli user, I want the export command to support all of the msg library's format (NONE, MF1 and MF2) options when exporting to XLIFF 2.2, so that I can export messages of all formats.
   • The format property should be preserved in the XLIFF 2.2 unit type attribute.
   • MF1 ICU plural/select messages should be converted to the XLIFF 2.2 PGS module (pgs:switch / pgs:case) on export, analogous to how MF2 .match messages are handled today.
2. As a msg-cli user, I want the import command to support all of the msg library's format (NONE, MF1 and MF2) options when importing from XLIFF 2.2, so that I can import messages of all formats.
   • The format property should be taken from the XLIFF 2.2 unit type attribute.
   • PGS-structured units whose format is MF1 should be reconstructed as ICU MessageFormat 1 plural/select strings on import.