Fix for PropertiesFileTransformer breaks Reproducible builds in 8.1.1

[agascon]

Closes GradleUp#858.

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Please have a look, added a test (which should fail with 8.1.1) and a fix on CleanProperties.

Removing the timestamp which default Properties class is adding could be tricky. I changed the previous mechanism to be bit more flexible (was not working either as some blank comment line is added now), but either way don't know if is a good approach. Please check

[Goooler]

This Date is related to your locale, how can we make sure the device locale is matched with the jar locale?

[agascon]

The idea of this is to just remove the comment lines which include the timestamp, which is generated when the properties file is written, so I assume locale is the same. Timestamp is not coming from other jar files. Either way I agree is a bit tricky.

Another option could be try to parse the date to see if it's a date or not, or maybe keep it simple and strip all comment lines.

Probably these changes are a mitigation as the real solution should come from the component writing the properties file, but anyway is more solid than the previous one which was removing only the first line.

[Goooler]

Timestamp is not coming from other jar files.

In this case, seems the fix is solid.

Another option could be try to parse the date to see if it's a date or not

In this case, seems we still have to determine the real locale is.

[Goooler]

I've published this in https://github.com/Goooler/shadow/releases/tag/v8.1.8