Fix Sentry interfering with MAUI's focus events

[mattjohnsonpint]

Fixes #1886

We were binding to Microsoft.Maui.Controls.VisualElement.FocusChangeRequested via reflection. That particular event has a handler that requires setting e.Result = true in order to not block the focus request. Unfortunately, the default is false (ouch!).

FocusChangeRequested is marked with [EditorBrowsable(EditorBrowsableState.Never)], indicating it's not meant for public consumption. We probably shouldn't have been attaching to it at all.

Fixed this in two ways:

• Changed the reflection-based event handler to not hook any events marked with EditorBrowsable (unless its param is Always)
• Added non-reflection-based event handlers for VisualElement so we can better control the specific events from that type.