Prior to this change, `TargetPane` passed `isRtl` to
`TargetPaneComponent` which then passed it into a `div`, causing the
warning below. Since `TargetPaneComponent` doesn't currently use `isRtl`
so there's no need to pass it in. If `TargetPaneComponent` starts
needing `isRtl` then we should adjust it to not pass that property to
any DOM elements.

The console warning in question is 57 lines long and starts with:

Warning: React does not recognize the `isRtl` prop on a DOM element. If
you intentionally want it to appear in the DOM as a custom attribute,
spell it as lowercase `isrtl` instead. If you accidentally passed it
from a parent component, remove it from the DOM element.

This indicates the current state, lets the user exit without changing
state, and lets the user change state any time they want.

This change also improves RTL support in the telemetry modal.

If `onClickAbout` is a callback, or is not provided, then behavior is
the same as it was before this change. If the value is an array of
objects with `title` and `onClick` properties, the "About" button will
now open a menu with those items.

TODO: support `FormattedMessage` for the menu item titles.