Expression evaluator for Scala IDE

Expression evaluator for Scala IDE

Implementation of expression evaluator and conditional breakpoints based on JDI.

Conditional breakpoints could be set in standard Eclipse debug window, for expression evaluator there is separate view. Both work with "new Scala" debug launcher.

Both allows user to evaluate any Scala expression in context of some breakpoint during debug. Expression is transformed in multiple phases and evaluated using calls to remote debugged machine and result is fetched back to user.

Because of complexity of Scala language, implementation details of JVM platform and necessity for manual evaluation not all Scala features are supported yet. Full list of features is available in `EXPRESSIONS.md` file.

Because of huge size of this PR we will contact you about making an introduction call to what had been done and how we approached it.

Lastly, the below disclaimer is required by the lawyers:

THE FOLLOWING DISCLAIMER APPLIES TO ALL SOFTWARE CODE AND OTHER MATERIALS CONTRIBUTED IN CONNECTION WITH THIS SOFTWARE:
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ONLY THE SOFTWARE CODE AND OTHER MATERIALS CONTRIBUTED IN CONNECTION WITH THIS SOFTWARE, IF ANY, THAT ARE ATTACHED TO (OR OTHERWISE ACCOMPANY) THIS SUBMISSION (AND ORDINARY COURSE CONTRIBUTIONS OF FUTURES PATCHES THERETO) ARE TO BE CONSIDERED A CONTRIBUTION. NO OTHER SOFTWARE CODE OR MATERIALS ARE A CONTRIBUTION.
I could do that but by inlining it inside block (of course to avoid creating fields from temp variables). Right now (in newer version) I changed this method's name to quite long "initContextMenuAndReturnLineNumbersItem" and used it directly in definition of lineNumbersItem without using var and null. Is it ok for you? (Menu itself should be disposed by parent so we don't need a reference to it)