Allow usage of Java Single File Launcher in non-Java projects

[jtulach]

• work on ProjectManager.findProjectOrFallback API #9650 revealed incorrectness of enablement check

... Java single-file support checks for FileOwnerQuery.getOwner(file) == null (SingleSourceFileUtil.isSupportedFile, and MultiSourceRootProvider for the classpath). So loose .java files in an opened non-Java project....

• When Java single-file support checks for FileOwnerQuery.getOwner(file) == null then it disables itself in (for example) C++ projects
  • checking that I am in no projects is not the right check and has to be changed
  • the right question is: Am I outside of a Java project?
  • per mutual agreement it: the right check is

Enable when not in a project with a Java SourceGroup

• this PR changes the check, so the support is enabled in C++ light projects (for example)

It Works now!

[neilcsmith-net]

Glanced through but not tested as yet. Looks good for that, thanks. My original suggestion was whether a file was within a Java SourceGroup. However, that might trigger issues with other project queries (eg. classpath), so what you have makes sense, is safer, and doesn't preclude looking further later if we need to.

Have you tested with a Maven parent (POM) project? If it works fine in there, it probably addresses some of the usages that would be nice to support in Java projects anyway.

Is the test dependency on SVG really needed?

[jtulach]

@neilcsmith-net wrote:

Is the test dependency on SVG really needed?

• No. Good catch.
• the dependency was only needed in ProjectManager.findProjectOrFallback API #9650
• as the FallbackProject there was using .svg in its getIcon
• we can remove it from this PR - gone in 7dcaf8e

[jtulach]

Have you tested with a Maven parent (POM) project? If it works fine in there...

Yes, it seems to work.

Is the test dependency on SVG really needed?

No, it is not needed. Removed.

[lahodaj]

Looks sensible to me. Minor style comment inline.