An xref that references page ID with a version but no file extension fails to resolve

The following xref fails to resolve:

xref:2.0@path#[link text]

This happens because the . in the version number is interpreted as a file extension, which causes the .adoc to not be appended.

An attempt was made in Antora 2.3 to remove the logic that automatically adds .adoc to a resource ID in the page family. This was done to support other file extensions. However, the logic that was added to retain support for a page ID without a file extension is failing in the above case.

The old logic in parseResourceId should be restored, except it should only add .adoc if . is not present in the relative path (previously it would check for .adoc). That way, we can have both the old and new behavior until the .adoc file extension becomes required in Antora 3.0.