Basically what happened is in Arduino IDE 1.6.5 they switched to using the RSyntaxTextArea editor for some reason. The new editor doesn't support the previous behavior of double click on a bracket highlighting the bracket contents. I personally don't find that feature very useful but the user who submitted that issue report was very upset and kind of went on a campaign for months trying to get something done about it. So I see two different approaches to getting the feature back:
Change the Arduino IDE editor to something that does support that feature. I'm not sure how standard this behavior is so this may or may not be difficult to find. You would either need to convince the Arduino developers to do all the work of making the change, which may be difficult or impossible since they seem to be happy with using RSyntaxTextArea, or you could do the work for them and submit a pull request. Submitting the pull request would greatly increase the chances of the change being made but there's no guarantee so if this is going to require a lot of work on your part you might want to first submit a proposal, either as an issue on GitHub or on the developers mailing list, to get a feel for how it will be received.
The other approach is to add that behavior to RSyntaxTextArea. Again you could try to convince the RSyntaxTextArea developers(or another interested party) to do the work for you or you can do the work, submit a pull request, and then hope you can convince them to merge it. After RSyntaxTextArea has been updated you would just need to get the Arduino developers to update to the new version of RSyntaxTextArea.
Although the loss of the highlighting feature is not something that affects me I do understand that it's very frustrating for people who previously relied on a feature like this to see it suddenly disappear for no good reason. I was very upset by the change to RSyntaxTextArea because of the idiotic automatic closing bracket behavior that was added so I would very much support the change to a different editor that either has this behavior optional or completely removed.
The other option you have is to use an external editor(File > Preferences > Use external editor) that works as you want and just use the Arduino IDE for things like uploading sketches, burning bootloader, Library Manager, Boards Manager, etc.