fix: reduce crashing, clarify documentation, and improve performance

[msmtamburro]

note: works around, rather than addresses existing architectural issues (#1031)
note: should be reviewed after merging this related PR #1050

Platforms affected

cordova-ios

Motivation and Context

This is related to #1031, in that I noticed the existing looping/reflection pattern in CDVWebViewEngine was copied, and I wanted to provide an example of how to allow consumers to explicitly be delegates, so that pattern, which crashes, does not make its way in to other pieces of code.

Description

The existing behavior, that CDVViewController can be a WKNavigationDelegate, was not obvious, so I documented it. While it would be more explicit to set the navigation delegate in the designated initializer (like is done with the WKWebViewConfiguration), I did not want to drastically change what's being done here. The existing behavior also loops through the plugins and uses reflection to see if any handle specific WKNavigationDelegate methods. The way this is done can crash (is crashing in my production app), as the list of plugins can change while this loop iterates.

What I did change:

• When a consumer has bothered to extend CDVViewController to be a WKNavigationDelegate, I've disabled the looping
• I cleaned up the looping to make it less likely to crash

Testing

I've tested the existing behavior:

• Overriding does not disable looping
• Looping does not appear to crash

I've tested the new behavior:

• Looping is disabled when overriding (making CDVViewController a WKNavigationDelegate)

Checklist

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

[codecov-io]

Codecov Report

Merging #1051 (0811908) into master (7e3402c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1051   +/-   ##
=======================================
  Coverage   74.82%   74.82%           
=======================================
  Files          13       13           
  Lines        1720     1720           
=======================================
  Hits         1287     1287           
  Misses        433      433           

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