fix: File contains no code even when there is code in prefixed modules

[MikaelMayer]

Fix #1838

This PR changes Dafny.atg so that it now reads (added part in bold)

if (membersDefaultClass.Count == 0 && defaultModule.Includes.Count == 0 && defaultModule.TopLevelDecls.Count == 0
&& (defaultModule.PrefixNamedModules == null || defaultModule.PrefixNamedModules.Count == 0)) {

That way, it does not trigger the warning "File contains no code" if there are some prefixed modules inside the main module.
The original files that were testing this warning were actually testing when we accidentally put a comment that comments the entire file, and another file that does not actually contain code, so this PR is consistent with them.

[cpitclaudel]

Should this be in the release notes?

[MikaelMayer]

Isn't this the file RELEASE_NOTES.md ? Note how in 1 commit, I was able to predict the pull request number :-)

[cpitclaudel]

I meant that maybe this should not be mentioned in the release notes?

[MikaelMayer]

Oh I got your comment. Yes I think it can reasonably go there.

[MikaelMayer]

We can always decide to remove it later, right @fabiomadge ?

[cpitclaudel]

Sure

[fabiomadge]

I think making the call now is useful. The point of preparing the notes is, that we don't need to think about them at release time.
In this case I think that this is user facing and has a place in the notes. I wouldn't object to later aggregating it under something like:

##Resolution
...

• Various fixes (fix: File contains no code even when there is code in prefixed modules #1840, ...)