[REGEDIT] split-drag-painting, can unduly be intercepted by keyboard events being sent to the treeview

Reproduction steps:

• run regedit
• make sure that the treeview has keyboard focus (not the listview!)
• select from the menubar "View / Split" . You are now in Splitter mode.
• drag the mouse in x (the slider will move)
• now DON'T click with the mouse button to end the Split-drag-operation, but instead do use the cursor up/down arrows to navigate a bit in the treeview (one or 2 keypresses are enough)
• now move the mouse again to the left or to the right
  you will see a mispainting of the splitter then

Observed result
the keyboard input is sent to the treeview
ReproductionVideo
drawing glitches of the splitter are the consequence

Expected result
no keyboard events should reach the treeview while being in splitter-dragging-mode, but the left- and right-arrow-keys should move the splitter and the mouse cursor then
no drawing dirt should occur

The bug is in Regedit.exe binary.
We must prevent the keyboard events being sent to the treeview, while being in drag-mode.

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