info: Platform support discrepancies

Which Keyman keyboard features are not completely portable? What is stopping us from making them portable?

Note: there are other issues for some platforms already present here.

Features:
- [ ] Mnemonic Layouts in Web, Touch
- [ ] Mnemonic Layouts in macOS, Linux (#14985, #3345)
- [ ] Keyboard Options in touch
- [x] Keyboard Options in macOS, Linux
- [ ] Keyboard Options Form in Web, iOS, Android, macOS, Linux (#2472)
- [ ] IMX
- [ ] Pickers
- [x] Blocked key combinations (per browser, KMW)
- [ ] `return` not supported in KMW (#1092)
- [ ] bitmaps not supported in OSK in KMW or Keyman for macOS
- [x] CSS styling not supported in popups on touch devices
- [ ] platform('hardware') is only supported in kmw. Keyman Desktop doesn't have an equivalent
- [x] notany() and context() is not supported completely in web, iOS, android (#917)
- [x] Caplocks state is not supported in web, iOS, Android, "Double Tap" on shift to enable "CAPS LOCK" state

The following issues are considered to bugs rather than feature discrepancies:
- [x] #13009
- [x] #13276
- [ ] #15358
- [ ] #15342

Keywords: compatibility, consistency, kmn, js