[eclipse-pmc] API additions to jdt.ui

[Martin Aeschlimann <martin_aeschlimann@xxxxxxxxxx>]

Request for 2 new API constants used to decorate the image of 'volatile' and 'transient' fields.
JavaElementImageDescriptor is API and every supported decorations is represented by a constant. By adding the 2 new decorations we should also add the corresponding constants.

• JavaElementImageDescriptor.VOLATILE
• JavaElementImageDescriptor.TRANSIENT

Note that only fields can be 'volatile'
and 'transient' and these modifiers are quite rarely used. Most clients
use the JavaElementLabelProvider that will provide the new decorations
without any changes required by clients. See bug 6553 for the discussion
why it is safe to add these decorators.

GOALS/BENEFITS:
- support for 'volatile' and 'transient' image decorators for consistency
reasons
- for API consistency reasons all possible decorations
should be represented by a constant in JavaElementImageDescriptor

CORRESPONDING BUG(S):

https://bugs.eclipse.org/bugs/show_bug.cgi?id=6553

RISKS:

No risk, all API additions.

PERFORMANCE IMPACTS:

No performance impact