Codechange: Change scrolling_scrollbar to mouse_capture_widget, and dispatch OnClick() event if widget is not a scrollbar.

This allows any widget to support mouse capture.

Fix: Some code and comment typos

Found with codespell

Feature: Framerate display window (#6822)

Frame rate and various game loop/graphics timing measurements and graphs. Accessible via the Help menu, and can print some stats in the console via the fps command.

Fix: [OSX] Minor 2D scrolling fixes (#6793)

* Codechange: Check for scrollwheel_scrolling first when scrolling viewport instead of first setting normal values and then overwriting them.

* Fix #6558: [OSX] Reset 2D scrolling values when not scrolling to prevent unintended window focus changes

* Change: [OSX] Include initial scrolling movement when using 2D scrolling to make it more responsive

* Fix: [OSX] 2D scrolling not working when setting viewport scroll behaviour to use left mouse button

(svn r27900) -Change [FS#6568]: Remove the gap between windows when positioning them after opening.
-Fix: Make automatic window-positioning RTL-aware.
-Fix: Automatic window-positioning now uses GUI-scale/style dependent sizes/distances instead of fixed pixel values.

(svn r23525) -Codechange: make Window::flags4 WindowFlags instead of uint16, with only values known in WindowFlags (and move out 2 timers to their own variable)
-Codechange: rename Window::flags4 to Window::flags
-Codechange: move some non-inline functions from .hpp to .cpp