(iOS) Skip Cocoapods checkTool on non-darwin platform

[AdamLak]

Platforms affected

• host environment
• iOS xcode project generation

What does this PR do?

Ignore CocoaPods check and installation on non-darwin (macOS) platforms.

What testing has been done on this change?

Manual tests:

• cordova plugin add cordova-plugin-firebase-crashlytics
• cordova plugin rm cordova-plugin-firebase-crashlytics

Tested on docker-linux: "Debian GNU/Linux 9 (stretch)"

Tested on Mac OS X:

• ProductVersion: 10.15.7
• BuildVersion: 19H2

cordova-ios: npm test - the results are below

Description

On Linux: try to add a plugin with Cocoapods dependency, e.g.:

• cordova plugin add cordova-plugin-firebase-crashlytics

Cordova throws an error instead of skipping the pod version check.
With this patch, Cordova ignores checking and installing CocoaPods on non-darwin (macOS) platforms.

Checklist

• I've run the tests to see all new and existing tests pass
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[AdamLak]

Test results on Macbook:

The manual test is also completed.

[AdamLak]

Breaking changes:

https://github.com/apache/cordova-ios/pull/849/files#diff-90b3ce405bfd064ca284320d6b7b87a48eb392047134fc24f715b486dc6a6de7R70