closes: #1374 .
Use SPDX short-form identifiers instead of lengthy copyright
header to document per-file license and copyright.
This commit updates all files under src/ directory where applicable
as well as org.flameshot.Flameshot.metainfo.xml.
* Move calls to update outside of each input case
* Remove redundant checks when moving selection
* Handle selection clipping the same for each mode
* Fix typo in SelectionWidget enum
* Obligatory "I forgot to clang-format" commit
New improved selection code:
- Selection decopuled into a new class
- When you drag the selection against the limits it won't become
permanently smaller, it will "bounce" trying to recover its size.
If you drop it again it will adapt its size to the borders of the
screen.
- Fixed bugs in the button position algorithm.
- Implemented selection animations for future implementations.
