[Win32] Update images of tree columns upon DPI change

[HeikoKlare]

When moving a shell with a tree that uses images in any other than the first column to another monitor, those images will be lost in case the other monitor has a different zoom such that the UI is rescaled. The reason is that the DPI change handling for TreeItem does not consider the other images of the tree item at all.

This change explicitly resets all images of a tree item upon DPI change.

Contributes to #3075

Remaining limitation

One limitation is that if an item does not have an image set for the first column, there will be blank space where the image could be after rescaling. This will be fixed independently via:

• [Win32] Avoid faulty setting of image list at OS on Tree.setOrientation #3077

Before rescaling:

After rescaling:

This is, however, an issue that already happens now (without any rescaling) in case the item has a subitems that uses an image in the first column:

And it also happens if you set and then remove an image, like this:

item.setImage(imageColumn1);
item.setImage((Image) null);

[github-actions]

Test Results (win32)

   34 files  ±0     34 suites  ±0   4m 14s ⏱️ -33s
4 649 tests ±0  4 576 ✅ ±0  73 💤 ±0  0 ❌ ±0 
  174 runs  ±0    171 ✅ ±0   3 💤 ±0  0 ❌ ±0 

Results for commit 083bfa6. ± Comparison against base commit 9c79cf6.

♻️ This comment has been updated with latest results.

[HeikoKlare]

Merging this as it obviously fixes the missing image update (analogous to an Item's image via Item#handleDPIChange), was verified by the issue creator (#3075 (comment)) and should go into M3 for some testing before the release.