Freeze on Edge instantiation via BrowserViewer

[HeikoKlare]

Mirror ticket for:

• [Edge] Eclipse freezes when opening more than 2 png files in internal web browser via Ctrl+Shift+R eclipse-platform/eclipse.platform.ui#3104

It shall be analyzed ...

• why exactly the issue happens only with two BrowserViewers opened (explain the control and data flows)
• why the same does not happen in the WebKit implementations

Based on the insights the Edge implementation should be fixed. If that's not possible and we agree on that the alternative is reasonable, we might apply a local fix to BrowserViewer to do some initialization asynchronously (as pointed to in eclipse-platform/eclipse.platform.ui#3104 (comment)).