Fix regenerate tasks to reproduce files with UNIX line endings by default [LUCENE-8225]

The ant generate tasks currently always normalize line endings to the local conventions. This was required by Subversion. With GIT it depends on your local config, but we should really use unix endings by default (don't use autofix crlf on windows, as this breaks shell/cmd scripts).

The idea is:
- add a property which defaults to "UNIX"
- fix the CRLF tasks in ant's build to use it

If somebody really wants to use Git's autofixing, he needs to change the property in his lucene.build.properties.

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Migrated from [LUCENE-8225](https://issues.apache.org/jira/browse/LUCENE-8225) by Uwe Schindler (@uschindler)