On other operating systems, if you hold down Alt when you click to
expand part of a tree, it expands all of the children of the node
you clicked. This commit makes our TreeView act the same way :)
This was using internal_data beforehand, which relies on the internal
data to be distinct for different model indices. That's not the case for
example for SortingProxyModel. Using the model index directly makes tree
expansion work properly when using a tree table widget with a
SortingProxyModel.
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 *
