feat(developer): add model_info and keyboard_info build activities to kmc

Adds ability to build .model_info and .keyboard_info files to kmc. Note
that .keyboard_info building is currently a stub as the .keyboard_info
compiler has not yet been translated to TypeScript, which will come in a
subsequent PR.

Note that .model_info and .keyboard_info builds depend on the project
loader, as they reference both keyboard and package source files when
constructing the metadata files.

Also:
* Fixed a deep reference to KeymanDeveloperProjectFile.
* Split the project loader into a utility unit.
* Marked the .kpj fileType field as deprecated, as it is easily
  extrapolated from the filename, with the aim to remove it entirely
  from version 2.0 projects.

@keymanapp-test-bot skip