[MJAVADOC-751] No warnings for localized output

[sitepark-schaeper]

This PR offers a solution for ticket MJAVADOC-751.
When parsing the output of the javadoc executable the english locale is expected (see containsWarnings and isInformationalOutput). In order for these checks to work the locale should be forced to english.

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[elharo]

This needs a test.

This might be a temporary workaround, but longer term I wonder if there's a non-command line way to invoke Javadoc these days.

[sitepark-schaeper]

This needs a test.

How would one go about testing this? Do we execute a test that executes the javadoc executable and check wether the output is english? There would also have to be a german/japanese/chinese environment to execute this test in as doing so in only english environments seems redundant.

This might be a temporary workaround, but longer term I wonder if there's a non-command line way to invoke Javadoc these days.

In Java 8 it should be as easy as:

javax.tools.ToolProvider.getSystemDocumentationTool().run(in, out, err, args)

And in Java 9+:

java.util.spi.ToolProvider.getSystemDocumentationTool().run(in, out, err, args);

But if we do that than we cannot influence the output locale anymore as it will always use Locale.default() (see here) and therefore cannot parse it reliably.