mediawiki.util: Insert node before updating tooltip for accesskey

updateTooltipAccessKeys() uses the native accessKeyLabel property which,
in Firefox, isn't available until after the node is inserted into the
document.

Bug: 67946
Change-Id: I3b80174e2f5df1c9082d30607dbe9b63ede6b5b5
Merge "mediawiki.util: Insert node before updating tooltip for accesskey"