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

[Eli Zaretskii]

Another observation: any command that calls current_column, directly
or indirectly, will be very slow with long lines.  This includes
"C-x =" and column-number-mode, for example.

I installed a change to avoid calling current_column where possible,
but the problem is we have a bytecode which calls it, and it is
impossible to avoid the call because it could break some callers.
Perhaps we should expose the long-line-optimization flag to Lisp, so
that commands like what-cursor-position could refrain from calling
current-column.