feat(developer): add line number information for more kmw messages

Adds line number context for:
  * Error_VirtualCharacterKeysNotSupportedInKeymanWeb
  * Error_VirtualKeysNotValidForMnemonicLayouts
  * Warn_ExtendedShiftFlagsNotSupportedInKeymanWeb
  * Hint_UnreachableKeyCode
  * Warn_HelpFileMissing
  * Warn_EmbedJsFileMissing
  * Error_NotAnyRequiresVersion14

Line number metadata is not easily accessible where the following
messages are generated, so these are a potential future improvement:
  * Warn_OptionStoreNameInvalid
  * Error_NotSupportedInKeymanWebStore