Helpful output when using build.json

# Feature Request

## Motivation Behind Feature

Currently there is not feedback or output if your `build.json` is not even applied because the `ios` key is missing or similar problems. This can lead to frustrating debugging and error search.

## Feature Description
It would be nice if there was some feedback if something is wrong with your `build.json` file like a missing key, invalid JSON or similar.

Outputting what actions are taken as the result of the build.json (`buildOpts` that are constructed, `extraConfig` that is written) would also make it easier to discover the absence of wanted logging.

## Relevant Code

https://github.com/apache/cordova-ios/blob/da5b69d62f2732039e9c82e603a24e291b086847/bin/templates/scripts/cordova/lib/build.js#L121-L138
https://github.com/apache/cordova-ios/blob/da5b69d62f2732039e9c82e603a24e291b086847/bin/templates/scripts/cordova/lib/build.js#L181-L214

## Alternatives or Workarounds
None.

Read bin/templates/scripts/cordova/lib/build.js around lines 121-138 and 181-214 first, tracing how build.json is read and how buildOpts and extraConfig are produced. Done means invalid or unapplied configuration gives useful feedback and the resulting build actions are visible.

Written by the indexing model from the issue text.