The toolbar handlers were copied onto view.events as unbound functions, so
`this` inside them was that object literal rather than the BOMConfigurator.
They worked only because the literal also carried `frm`, and broke as soon as
a handler called a method the literal did not list: get_item_code, added when
the tree started keying nodes on the row name, threw
"this.get_item_code is not a function" and killed Add Raw Material, Add Sub
Assembly and Convert to Sub Assembly.
Assign the instance instead of a hand-maintained whitelist. Every method is
reachable, `this.frm` keeps working, and no future method can be forgotten.
Fixes#57773
(cherry picked from commit 097ce0f348)
281e92fb6e