For all non-.java source files that I know of, the
tooltip for the source editor tab gives the full
path to the disk file, if available. (Else the
relative path within the filesystem, and the
filesystem display name.) For Java sources, it
shows e.g.:

some.pkg.Class [java] in /home/me/src

which is weird and inconsistent; would prefer simply

/home/me/src/some/pkg/Class.java

or if there is no disk file,

some/pkg/Class.java in /home/me/src.jar

History: once, all files showed the "package.Class
[ext] in Filesystem" syntax, but this was changed
to show the file path to avoid seeming too
classpath-specific. Was not changed for .java however.

Impl should be trivial: delete
JavaEditor.messageToolTip and matching bundle keys.