Fix/Persist inappbrowser webview across different calls

[nflsilva]

Platforms affected

• iOS
• Android

Motivation and Context

A particular customer requested support because they were not able to open a specific webpage using the InAppBrowser.
After some investigation, we concluded that this was an issue regarding the WebView session being destroyed on different calls to the Cordova action.

Description

We changed the code so only 1 WebView is created during all plugin lifetime. We keep in memory a reference the the same webview.

Testing

These changes were tested with MABS7

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

[mikko-n]

Hello,
I've been wondering if this pull request is going to be reviewed and merged? It's been a while now...
ping @CarlsCorrea @alexgerardojacinto @andregrillo @nflsilva