Project contained translations break when module is moved

Problem/Motivation

When a project contains translations and this is done like described in the docs, and the project is relocated, the translation import will break.

From Interface translation properties:

Custom modules which contain new strings should provide po file(s) containing source strings and string translations in gettext format.

Example .info.yml file properties for a custom module with a po file located in the module's folder.

'interface translation project': example_module
'interface translation server pattern': modules/custom/example_module/%project-%version.%language.po

Note the hardcoded modules/custom here. This will break if the module is moved.

Proposed resolution

Add a placeholder that resolved to the project location.

Remaining tasks

Review, discuss, commit.

User interface changes

None.

API changes

We provide an additional placeholder for the mymodule.info.yaml 'interface translation server pattern'.

Data model changes

None.