feat(developer): warn when compiling keyboard with unassigned codepoints 🙀

[srl295]

give a warning when in "CLDR repo mode" for unassigned codepoints when compiling.

• ignore PUA, those are fine. (they are assigned)

• feat(core): warn on unassigned codepoints when loading keyboard 🙀  #9464

• feat(core,developer): detect bad unicode in kmxplus 🙀  #9446

• feat(developer): ldml scancodes 🙀  #9403 also discusses "cldr repo mode"

• need separate field for unicode version in the warning message.