Don't disable *TRACK* in ";type tool" plugins

[SteveDaulton]

Your idea

If a Nyquist script / plugin has the header:
;type tool
then the variable TRACK is disabled by Audacity.

Although TRACK only represents a snapshot of the selected audio at the time that the Nyquist script is launched, it can still be very useful. Working around the absence of TRACK can be very complicated.

Problem to be solved

It is often much easier to get information about the initial state of a project by using the properties of TRACK than by other means, but often it is necessary to use complicated "other means" just to work around this restriction.

Example:
To split a selected track exactly in half.
This code would work if TRACK was available in a ;type tool plugin:

;type tool
(let* ((start (get '*track* 'start-time))
       (end (get '*track* 'end-time))
       (mid (/ (- end start) 2.0)))
  (aud-do-command "SelectTime:"
                  :start mid
                  :end mid
                  :relativeto "SelectionStart")
  "")

but because TRACK is disabled, it's necessary to use two Nyquist scripts plus two additional scripting commands, wrapped up in a macro:
(scroll the code block to see the full code)

SelTrackStartToEnd:
NyquistPrompt:Command=";type analyze\n(setf *scratch* (list (get '*track* 'start-time)\n                     (get '*track* 'end-time)))\n\"\"" Parameters=""
SelTrackStartToEnd:
NyquistPrompt:Command=";type tool\n(let ((mid (/ (- (second *scratch*) (first *scratch*)) 2.0)))\n   (setf *scratch* '*unbound*)\n   (aud-do-command \"SelectTime:\"\n                   :start mid\n                   :end mid\n                   :relativeto \"SelectionStart\")\n   (aud-do \"Split:\")\n   \"\")" Parameters=""

Prior art

No response

Additional context

No response