LED-Palette-Theme: Defer requesting a slice as late as possible

Previously we requested a slice in `onSetup()`, but this had a major,
problematic implication: if we went from a sketch with `EEPROM-Keymap`, but
withot `LED-Palette-Theme` enabled to one with it, the EEPROM layout was not
compatible, no matter what the order of plugins in `KALEIDOSCOPE_INIT_PLUGINS`
were. This happened because `EEPROM-Keymap` requested space *after* `onSetup()`
already ran.

To fix this issue, request a slice in `.reserveThemes`, only if we didn't
request a slice yet. This way the EEPROM layout is decided by the order of
initialization in `setup()`, and we do not sneakily steal a slice in
`onSetup()`.

This is required to address keyboardio/Chrysalis#270.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

NEWS.md

@@ -144,6 +144,8 @@ The [Redial](doc/plugin/Redial.md) plugin was simplified, one no longer needs to
 
 The [LED-Palette-Theme](doc/plugin/LED-Palette-Theme.md) had to be changed to store the palette colors in reverse. This change had to be made in order to not default to a bright white palette, that would draw so much power that most operating systems would disconnect the keyboard due to excessive power usage. With inverting the colors, we now default to a black palette instead. This sadly breaks existing palettes, and you will have to re-set the colors.
 
+We also changed when we reserve space for the palette in EEPROM: we used to do it as soon as possible, but that made it impossible to go from a firmware that does not use the plugin to one that does, and still have a compatible EEPROM layout. We now reserve space as late as possible. This breaks existing EEPROM layouts however.
+
 ### EEPROM-Keymap changed Focus commands
 
 The [EEPROMKeymap](doc/plugin/EEPROM-Keymap.md) plugin was changed to treat built-in (default) and EEPROM-stored (custom) layers separately, because that's less surprising, and easier to work with from Chrysalis. The old `keymap.map` and `keymap.roLayers` commands are gone, the new `keymap.default` and `keymap.custom` commands should be used instead.

src/kaleidoscope/plugin/LED-Palette-Theme.cpp

@@ -25,14 +25,10 @@ namespace plugin {
 
 uint16_t LEDPaletteTheme::palette_base_;
 
-EventHandlerResult LEDPaletteTheme::onSetup(void) {
+uint16_t LEDPaletteTheme::reserveThemes(uint8_t max_themes) {
   if (!palette_base_)
     palette_base_ = ::EEPROMSettings.requestSlice(16 * sizeof(cRGB));
 
-  return EventHandlerResult::OK;
-}
-
-uint16_t LEDPaletteTheme::reserveThemes(uint8_t max_themes) {
   return ::EEPROMSettings.requestSlice(max_themes * ROWS * COLS / 2);
 }
 

src/kaleidoscope/plugin/LED-Palette-Theme.h

@@ -41,7 +41,6 @@ class LEDPaletteTheme : public kaleidoscope::Plugin {
   EventHandlerResult themeFocusEvent(const char *command,
                                      const char *expected_command,
                                      uint16_t theme_base, uint8_t max_themes);
-  EventHandlerResult onSetup();
 
  private:
   static uint16_t palette_base_;