Added documentation about SWT's Autoscale methods

This PR adds the documentation about SWT's Autoscale methods and their
behavior

Author: ShahzaibIbrahim

docs/hidpi-support.md

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+# HiDPI Support in SWT
+
+This document (incompletely) describes certain parts of the HiDPI support in SWT for all platforms (Windows, MacOS, GTK).
+
+## Table of Contents
+
+1. [Autoscale Methods](#autoscale-Methods)
+
+### Autoscale Methods
+
+The `swt.autoScale.method` system property controls the method used to determine how to handle scaling of Images in SWT:
+
+- **`smooth`**
+
+- Uses anti-aliased / bilinear interpolation
+- Smooth edges, may appear slightly blurry
+
+- **`nearest`**
+
+- Uses nearest-neighbor interpolation
+- Edges appear jagged or blocky
+
+
+**Example usage:** To configure the smooth scaling, set the system property to one of the above, e.g. *-Dswt.autoScale.method=smooth*
+
+**Default Behavior**: 
+
+- `GTK`: Uses smooth scaling only when deviceZoom is an integer multiple of 100% (100%, 200%, …). Otherwise, SWT falls back to nearest.
+- `Windows`: Uses smooth scaling only if monitor-specific DPI scaling is enabled (Per-Monitor DPI awareness). Otherwise, SWT uses nearest.
+- `MacOS`: Never uses smooth scaling.