qml: fix drop shadow scaling
This fixes shadows not being scaled correctly when item size changes or when DPR changes
the issue is illustrated bellow, effect is shown without the blur effect applied to make it easier to the issues
| before | now | |
|---|---|---|
| bad aspect ratio |
|
|
| bad shadow scaling (large source) |
|
|
| bad shadow scaling (very small source) |
|
|
Image also scales correctly with DPR
| 1x | 2x |
|---|---|
 |
 |