Read classpath for the file, rather then for the directory, to help with cases where files have classpath, but directories don't.

[lahodaj]

When debugger evaluates watches, it sometimes interprets the watch, but if the watch is too complex, it will synthetize a class with the watch, compile, load and execute it.

When compiling the class, it will gather the ClassPath, but it bases that step on the source root, not on the relevant file. As a consequence if ClassPath for file and directory differs, there may be a problem when compiling the synthetized class. This may happen e.g. for OpenJDK tests, that don't have ClassPath for source roots.

The proposal here is to simply read the ClassPath from the relevant file, not the directory.

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[lkishalmi]

Seems reasonable.