Provide a way for speech output to be written to a file

[jteh]

It might sometimes be useful for all speech output to be written to a file. This could be done in one of two ways:

• As part of the "display" synth driver; or
• As an option independent of synth drivers.

I am uncertain as to the best approach to take. This needs to be discussed.

[aleksey_s]

it is already done with nvda logging system, all spoken text is written to nvda log.

[mdcurran]

As this is already done via NVDA's log file, for now I think this can be closed. We can always open it later if there are problems with this approach.