Token highlighting for identifiers with Unicode

Hi, Chris,

This is a followup on Issue #1525. That one fixed the colour deviation of Unicode characters in the display of identifiers (red instead of the surrounding black for ASCII).

In the original report I also mentioned the background colour for highlighting all the occurrences of the identifier currently under the cursor. While the foreground colour got fixed in #1525, the identical-token-highlighting (with background colour) did not.

To illustrate: #1525 fixed the token colouring issue, but not the "token highlighting" (of token under cursor) (with light-green background)

(With the cursor on `betáp`, the expectation would be to highlight all of it, and to not highlight the `bet` part of `betűkkel`).

I created this separate issue, because I suspect my comment on the already closed issue might go unnoticed.

I'd totally understand if this would be a a "won't fix" (because of Code Mirror dependency) or low priority, however, I figured given the experience gained with #1525, maybe this turns out to be a similarly minor patch, and someone just has to find the place where the regexes are defined. (I think it's strange to begin with, that the code is not shared with the foreground colour).