refactor!: Easy deprecation cleanups

[dpogue]

Platforms affected

iOS

Motivation and Context

Closes #1428.

Description

• Added deprecation annotations to things we want to discourage people from using (some of these can be removed in Cordova iOS 9)
• Remove some conditionals for iOS versions pre-11 and dead code
• Change CDVPlugin's viewController from a UIViewController* to a CDVViewController*
• Move a webview engine-related delegate to a header that makes more sense

Testing

Unit tests pass.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• 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)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.35%. Comparing base (c8e126d) to head (7c10750).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1455   +/-   ##
=======================================
  Coverage   78.35%   78.35%           
=======================================
  Files          16       16           
  Lines        1825     1825           
=======================================
  Hits         1430     1430           
  Misses        395      395           

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[erisu]

LGTM

Tested with:

• Xcode 16 (beta 5) & iOS 18 (beta 5)
• Cordova default application and confirmed that the Device is Ready is displayed.
• Mobile spec to run against all of Apache Cordova's plugins.