added true center option for fullscreen center mode (#19593)
#19462
Summary of the issue:
A tester wanted to have a true center mode for fullscreen magnifier
Description of user facing changes:
Users will now be able to set a "use true center" in settings to change the behavior of the fullscreen center mode:
Mouse will stay at the center of the screen at any time, no more clamping at the edges
Description of developer facing changes:
added a config and a function to access to it to calculate the coordiantes of the fullscreen window
