feat(developer): kmc-generate and kmc-copy consolidation

Consolidating TODO lists from #11014, #12555

## TODO-GENERATE for kmc-generate, from #11014
- [x] #12954
- [x] #12957
- [x] documentation --> #12647
- [x] #12965
- [x] #12961
- [x] #12959
- [x] #13045
- [ ] 19.0: keymanapp/help.keyman.com#1335 -- update kmconvert ref
- [ ] 19.0: generate icons (keyman-keyboard-generator.ts TODO-GENERATE, also tests)
- [ ] 19.0: UI in Keyman Developer (to replace existing kmconvert-based systems)

## TODO-COPY for kmc-copy, from #12555
- [x] documentation --> added to #12586, just cloud docs reqd)
- [x] #12972
- [x] #12975
- [x] #12978
- [x] #12981
- [x] #12983
- [x] #13060
- [x] #13073
- [ ] 19.0: additional testing (TODO-COPY)
- [ ] 19.0: copy all files in the folder and subfolders from cloud sources, even when using a 1.0 project type (also for github sources?)