AgX refactoring and preset changes

[kofa73]

Technical changes:

• gui_changed reentrancy protection via early return if darktable.gui->reset is set
• don't call gui_update from gui_init (agx: Fix crash during initialisation #19745 (comment))
• call gui_changed after gui_update (agx: Fix crash during initialisation #19745 (comment))
• deduplication / consistency:
  • extracted showing/hiding dynamic widgets into _update_redraw_dynamic_gui
  • extracted pivot slider configuration into _update_pivot_slider_settings

Defaults and presets

• based on own experience and user feedback (https://discuss.pixls.us/t/more-punchy-contrasted-look-in-agx-by-default/55279/), I've made the defaults more contrasty; the new default contrast and toe/shoulder power are now similar to the 'sigmoid look' that people have grown accustomed to.
• added 'sigmoid-like' presets that very closely exactly match the tone curve of sigmoid with its default params and the 'smooth' preset. For 'sigmoid-like|smooth', hue preservation is set to 100% (like in sigmoid's own 'smooth' preset), and primaries are set like in sigmoid (using the 'smooth' set). For 'sigmoid-like|default', hue preservation remains at 0% (like in sigmoid), however, unlike sigmoid (which uses unmodified primaries), Blender-like primaries are used (we don't want to disable the core feature).
• I only kept 'punchy' for Blender, as the other presets are quite contrasty already.

UI:

• primaries selection remains visible even when "disable adjustments" is checked (disable adjustments is about rotations and in/outset, not about the base primary)
• use dt_ui_label_new to fix Agx module makes window too big #19970
• reworded the toe/shoulder power tooltip, which often led to questions, to explain that it's not an error or bad setting that must be fixed

Minor:

• removed soft limits that matched hard ones
• gboolean defaults shouldn't be 0.f and 1.f and min/max make no sense
• colour -> color

This PR replaces #19745

[TurboGit]

@kofa73 : This is too big for 5.4.1 and also contains strings changes which cannot be integrated into 5.4.1.

Would it be possible to extract from this the fixes, if I'm not mistaken those are:

• gui_changed reentrancy protection via early return if darktable.gui->reset is set
  don't call gui_update from gui_init (
  agx: Fix crash during initialisation #19745 (comment))
• call gui_changed after gui_update (
  agx: Fix crash during initialisation #19745 (comment))
• use dt_ui_label_new to fix Agx module makes window too big #19970

TIA.

[kofa73]

OK, I'll extract those into a separate PR tomorrow. Thanks for the feedback.
I consider this also to be a fix:

primaries selection remains visible even when "disable adjustments" is checked (disable adjustments is about rotations and in/outset, not about the base primary)

[kofa73]

#20122 for 5.4.1