Allows to bind a click handler to a TestHint.

When a mobile test wants to click an UI element it must be able to
locate it through the accessibility layer. Now the problem with that is
that there is currently no uniform way for finding element on both iOS
and Android. This problem is solved by TestHint component which takes
an id parameter which then can be specified in the corresponding java
TestHint class in jitsi-meet-torture to easily find it. By being able to
add a click handler to a TestHint, it's possible to duplicate original
handler under nested TestHint and then find it easily on the torture
side.

Adds the logic to render TestHint only when the test mode is enabled
in order to be able to put independent TestHints in other places than
the TestConnectionInfo component.