bug#56682: Fix the long lines font locking related slowdowns

[Gregory Heytings]

> > But is there an efficient way to determine if that the buffer doesn't 
> > include any R2L characters?
>
> Not without searching the buffer, not that I know of.

Thanks, that's what I thought.

> > > If you remove the 3 closing braces/brackets at EOB and the 
> > > corresponding opening braces/brackets, does navigation become 
> > > significantly faster?
> >
> > Yes, removing the 3 brackets at positions 1, 22, 23 and 19538, 19539 
> > and 19540 solves that problem.  In fact, just removing the brackets at 
> > 1, 22 and 23 solves that problem.  You can see the same problem in 
> > dictionary.json, just removing the first character makes C-n and C-p 
> > faster at BOB.
>
> Stephen said it had a much smaller effect than inhibiting the BPA. But 
> yes, very long bracketed text segments could be a problem.

I'm not completely sure he did indeed remove those three brackets. 
Stephen, can you remove the three characters at positions 1, 22 and 23, 
and try again?  These are the first two '{' and the first '[' characters 
in the buffer.