fdo#65586: Add tools tips in Math Elements Dock

Change-Id: I304ba9fe0a97f85424d0eb0ee87bf3b4b58179f4
Reviewed-on: https://gerrit.libreoffice.org/6540
Reviewed-by: Marcos Souza <marcos.souza.org@gmail.com>
Tested-by: Marcos Souza <marcos.souza.org@gmail.com>