IDLE bindings for scrolling using buttons 4 and 5 should only apply to X11

[chrstphrchvz]

Bug report

On X11, vertical scrolling is conventionally done using events for mouse “buttons” 4 and 5. But on Win32 and Aqua, which have a dedicated event for scrolling (<MouseWheel> in Tk), buttons 4 and 5 correspond to additional hardware buttons present on some mice. Tk 8.6 and earlier do not abstract away these platform differences, so bindings in IDLE for scrolling should ignore buttons 4 and 5 on non-X11.

Accordingly, idlelib.idle_test.test_sidebar.ShellSidebarTest.test_mousewheel should be revised to check the windowing system, so that it correctly distinguishes between Aqua and XQuartz (which sys.platform == 'darwin' does not do), sends button 4/5 events on X11 only, and sends <MouseWheel> with the correct sign for delta on Aqua.

Tk 8.7 (TIP 474) will change mouse events to be consistent across windowing systems. This requires further revisions, but I imagine it is better to separately address issues for Tk ≤ 8.6 first.

Linked PRs

• gh-103820: IDLE: Do not interpret buttons 4/5 as scrolling on non-X11 #103821
• [3.12] gh-103820: IDLE: Do not interpret buttons 4/5 as scrolling on non-X11 (GH-103821) #114901
• [3.11] gh-103820: IDLE: Do not interpret buttons 4/5 as scrolling on non-X11 (GH-103821) #114902

[terryjreedy]

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