Since we keep a stack of command combos, let's call entries on the
stack "Combo" instead of "UndoCommandsContainer".
And since it has a vector of commands, let's call it "commands"
instead of "m_undo_vector".
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
