completion results for non-loaded classes

[eugen-yakovets]

• Add scan command for scanning all classes in classpath (non only already loaded by classloader)
• Use classpath scan result for command completion

[gharrma]

Thanks for the PR. I haven't look too deeply at the implementation, but I did try out the feature.

I think the performance of scan is a blocking issue, unfortunately. For me at least it froze the IDE for a few minutes and triggered low-memory warnings :). I could increase my heap size, but ideally it shouldn't be needed. Do you think it is possible to improve the performance? Or is the problem just that there are so many classes to scan through?

Note, I also noticed performance regressions for other commands, even without using scan at all. It seems there is some additional reflection happening ClassMethods.tryCreate now.