Support disabling view accessibility features

### Problem description

Currently, some apps may spy on accessibility events emitted by the views of a Tabris.js app. This may compromise the security of a Tabris.js app, since sensitive user input may get unexpectedly stolen by an attacker service. See https://android.jlelse.eu/android-accessibility-75fdc5810025 (note: the article recommends using `setImportantForAccessibility()`, however using this setting is not sufficient, since an attacker accessibility service may use the flag `FLAG_INCLUDE_NOT_IMPORTANT_VIEWS`)

### Expected behavior

Provide an API to selectively disable those accessibility events on per view basis, e.g. by using an accessibility delegate overwriting `sendAccessibilityEvent()`, `sendAccessibilityEventUnchecked()` and `onRequestSendAccessibilityEvent()`.

### Environment

- Tabris.js version: 2.5.1
- OS: Android