Add EEPROM and focus support to ColormapOverlay

[EvyBongers]

Quick attempt to implement focus support in ColormapOverlay. I feel this should work, but I don't have my keyboard with me right now, so any debugging I'll have to do later.

[EvyBongers]

colormap.overlay seems like the most logical focus command to me. Let me know what you think.

[obra]

@EvyBongers did you end up testing this on hardware?

[EvyBongers]

I completely forgot about this. I'll see about testing it today

[EvyBongers]

So, I finally got around to testing this. The command returns the palette indexes as expected, but setting the indexes doesn't yet work 🤔

[EvyBongers]

So, I dug a little deeper to see what I was missing. I thought I had a quick fix by calling on ::LEDPaletteTheme.themeFocusEvent(), but the internal logic of the plugin never actually used LEDPaletteTheme to store its data because it was never intended to work as a theme.
Looking at #1416, it seems to me that the third PR that we discussed there was never created, so unless we want so implement a read only version here, this effort is going to have to wait until EEPROM support is added to Colormap-Overlay.

The confusing part is that Colormap-Overlay (seemed to) need to call ::LEDPaletteTheme.reserveThemes() in order to work with the palette, even though it never uses any of the theme logic. It's been ages since I implemented that part and I don't remember why I needed to add that call to reserve themes nor whether it's actually needed for the plugin to work with the palette at all.

Closing this for now

[EvyBongers]

Reopened because EEPROM supports needs to be added anyway and EEPROM and focus support should land together.

[EvyBongers]

Just found a comment about this on Discord. Cross-posting to have all of this together.

#1434 will need quite a bit of work yet, I think. My first attempt to make focus work for colormap overlay settings simply passed through the handling of the focus event to ::LEDPaletteTheme.themeFocusEvent(). I had a proper look at that today and I'm pretty sure that isn't going to work, or at least it isn't sufficient. That's partly because (iirc) I needed to reserve at least one theme to get ::LEDPaletteTheme.lookupPaletteColor() to work. However, the plugin doesn't store any other data in a theme. That means that I will either have to find a way to have the plugin work with themes or I'm gonna have to implement a second or different means for handing the focus command