Just to be clear: there are two fixes.
The first, real fix is the fix shown in the above issue, which is a fix to Eclipse itself. This fixes the focus handling properly. This is fixed in Eclipse 4.3. I tried downloading a build of 4.3 and I confirmed that the bug is fixed. However, there were several other issues with the 4.3 nightlies, so I wouldn't recommend switching at this point.
I also don't think that you can just transplant one of the .jars from 4.3 and drop it into 4.2 and that it will necessarily work. I haven't tested that, but you could try it. It looks like the fix is in one of the swt jars.
However, in ADT 21, I've added a workaround. It's a very dumb workaround, but a workaround nonetheless. When the IDE discovers that focus handling is broken (because it throws a null pointer exception at a certain point), it traps that event and instead opens up the customizer. This has the net effect of making a click on a text field (to start editing) have the effect of clicking on the adjacent "..." button instead. This isn't great since it means that you get a popup dialog when you want to change for example a text attribute, but it's preferrable to the current situation where you click and nothing happens and you click and you click and you click (and some users might not even realize the workaround of clicking on the customizer). However, since this behavior can definitely be perceived as annoying, the popup also contains a 3 line red font message explaining that it's a Mountain Lion specific Eclipse bug that will be fixed in Eclipse 4.3. I'm even hoping for a backport to 4.2.2; we'll see.
-- Tor