Computes a default source lookup path for Java applications.
The source path provider associated with a launch configuration is consulted
to compute a source lookup path. The source path provider is determined
by the
ATTR_SOURCE_PATH_PROVIDER launch configuration attribute,
which defaults to the
StandardSourcePathProvider when unspecified.
The source path provider computes a collection of
IRuntimeClasspathEntry's
which are translated to source containers (
ISourceContainer).
Clients may subclass this class.