feat: support normalization in keyboards

**Is your feature request related to a problem? Please describe.**

Per Keyman Developer 14 release video feedback -- automatic normalization support would be very useful, that is both: handling NFC and NFD transparently in context, and targeting a specific normalization form for output.

**Describe the solution you'd like**

This would require changes to Keyman Core and KeymanWeb, along with appropriate flags in keyboards (for default output normalization) and possibly advanced user interface to allow for normalization mode selection.

**Describe alternatives you've considered**

It is possible to define multiple rules that handle NFC and NFD context, but tedious. It is more difficult to handle partially normalized context by defining multiple rules -- somewhat impractical.