This is consistent with the core Godot source code, and ensures the
license isn't detached from its original code when individual files
are distributed.
The [] operator of Basis was returning a reference to a temporary, so fixed it.
There was no * operator in Transform equivalent to the xform function, which is
not in line with GDScript behavior.
Also fixed remaining cases where Transform relied on the old behavior of the
[] operator of Basis (i.e. that it returns the row, not the column).
Rémi Verschelde
Hugo Locurcio
Marc Gilleron
Daniel Rakos
Bastiaan Olij
Karroffel