Add test for renamings.js

Is your feature request related to a problem? Please describe.
We have a new renamings.js file that we plan on using to help developers update easier. We need to make sure this files is formatted properly when it is updated. See google/blockly-samples#924 for more information.

Describe the solution you'd like
A test that is run during CI to check that the format of renamings.js is correct and valid.

Describe alternatives you've considered