[eclipse-pmc] Add new API constant: org.eclipse.osgi.service.datalocatio

[Thomas Watson <tjwatson@xxxxxxxxxx>]

GOALS/BENEFITS:
- Add a new filter constant used for acquiring the eclipse home location
service. An eclipse home location service has been defined to
allow clients to discover the location of the eclipse native launcher
installation. In p2, such a location is needed to provision such things
as the dropins, links and p2 folders.

AFFECTED BUGS:
- https://bugs.eclipse.org/bugs/show_bug.cgi?id=217351

RISKS:
- If we do not add a new constant, then clients will have to construct
their own filter strings to obtain the eclipse home location service.
- Other location services available have a filter constant, we should
be consistent and have a constant for the eclipse home location
service.

PERFORMANCE IMPACTS:
None.

Thanks.

Tom