fix: Avoid Crash Report: ConcurrentModificationException

[lempere]

Platforms affected

Android

Motivation and Context

Fix #924
We have a project with 31 plugins installed, in some devices like Huawei p30( or emulator Pixel_3-x86_64 android R) fail starting the app 4 of 10 times.
Showing the ConcurrentModificationException error from the webView.postMessage("splashscreen", "hide"); of the SplashScreen.java

Description

Tracking the #924 thread I found a code to avoid the error using .synchronizedMap. This was not enough the app still crash sometimes.
Then testing using the .forEach instead of the for (CordovaPlugin plugin : this.pluginMap.values()) works. No more ConcurrentModificationException were thrown.
A counterpoint is that .forEach is not available prior android 6 and a check version is needed.

Testing

npm run test
Found a device with launch problems. Start the app a lot of times with this pr code, no ConcurrentModificationException happens again.

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

[breautek]

Hi @lempere

We are working towards building a 9.1 release and would like to include this PR, are you able to rebase against current master and solve the merge conflicts?

[codecov-io]

Codecov Report

Merging #1073 (8e9764a) into master (19a5feb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1073   +/-   ##
=======================================
  Coverage   73.30%   73.30%           
=======================================
  Files          22       22           
  Lines        1768     1768           
=======================================
  Hits         1296     1296           
  Misses        472      472           

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[erisu]

LGTM

[breautek]

Thank you @lempere for your effort into preparing this PR and contributing to Apache Cordova.