This has been an unnecessary code path for a long time now and should be removed particularly because it triggers wasteful `stat` calls.
rdar://51523161
- Report accessor function definitions for stored properties as well
- Fix issue where a call to a computed accessor was not reported if its parent was a statement
- Take into account if the stored property is member or not to adjust the symbol kind for the accessor
The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.
SourceKit is disabled on non-darwin platforms.
