Starts to address #2039
Move FileProvider back to Keyman manifest and revert authority.
Added Toast notification if 3rd party app doesn't define FileProvider. (info pages fail to properly load)
For keyboards installed via keyboard packages, use the welcome.htm if it exists for keyboard information
- Update PackageProcessorTest to include CustomHelpLink info
- Renamed Welcome.htm to welcome.htm in test_resources/**/gff_amh_7_test_json.kmp.