All platforms: add structured feedback dialog

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

Daniel Yona (FPCC) suggests adding a feedback mechanism to Keyman (and FV Keyboards). The feedback should be guided, rather than completely freeform. The following categories of feedback were briefly suggested (but there may be others) - e.g. missing key, square boxes, malformed characters, improved key placement.

Depending on the category, there should be additional fields shown and or information collected. For example, if the app isn't working, an option to collect diagnostics should be included.