This adds support for the Tools in PixelPaint to use different cursors
within ImageEditor. For now most of them get the crosshair cursor since
it's the most fitting, but in the future we will want to add custom
cursors.
Previously m_constrain_angle could end up not being reset if the
keyup-event was lost, for example when opening a dialog. Instead check
the modifiers in on_mousemove().
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 *
