Add N&N for improved disabled icons

This contributes an N&N informing about the icon disablement algorithm
in SWT being improved and made configurable and the according removal of
the usage of pre-generated disabled icons.

See eclipse-platform/eclipse.platform.swt#1936

Author: HeikoKlare

news/4.36/images/disabled_icons_desaturated.png

@@ -100,6 +100,52 @@ <h2>Preferences </h2>
 					<h2>Themes and Styling </h2>
 				</td>
 			</tr>
+			<tr id="improvedDisabledIcons"> <!-- https://github.com/eclipse-platform/eclipse.platform.swt/pull/1936 -->
+				<td class="title">Improved Disabled Icons Generation</td>
+				<td class="content">
+					<p>
+						Up to now, disabled versions of icons usually were and had to be provided as explicit, separate image files.
+						In case no such icon was provided, an algorithm in SWT was used to generate a disabled icon. However, that
+						algorithm was very limited and produced hardly usable results.
+					</p>
+					<p>
+						The algorithm in SWT was now improved such that results are by default equal to the disabled version of the
+						icons that have explicitly been provided for the Eclipse Platform bundles. In consequence, those
+						pre-generated disabled icons are replaced with the usage of on-the-fly generated disabled versions of the
+						icons via the SWT algorithm.
+						This particularly includes the removal of <code>disabledIcon</code> in <code>plugin.xml</code> files and
+						setting the <code>disabledImageDescriptor</code> within code for <code>Actions</code>.
+					</p>
+					<p>
+						In addition, the algorithm for the calculation of disabled versions of icons became exchangeable. The
+						algorithm can be changed via the system property <code>org.eclipse.swt.image.disablement</code> with the
+						following options:
+					</p>
+					<ul>
+						<li><code>grayed</code> (default): produces a gray-scaled version of the icon, which is aligned with the
+							existing, pre-generated disabled versions of icons for Eclipse bundles</li>
+						<li><code>gtk</code>: produces an icon version that conforms with the default disablement algorithm of GTK
+						</li>
+						<li><code>desaturated</code> (preview): produces a desaturated version of the icon, comparable to the
+							<code>grayed</code> version but still keeping some color in it; the configuration of this option may be
+							subject to change in future releases of Eclipse</li>
+					</ul>
+					<p>
+						The following screenshots show the different options. The screenshot for the <code>gtk</code>
+					</p>
+					<p>
+						<img src="images/disabled_icons_grayed.png" alt="Disablement option 'grayed'" /> &nbsp<code>grayed</code>
+						(default)
+					</p>
+					<p>
+						<img src="images/disabled_icons_gtk.png" alt="Disablement option 'gtk'" /> &nbsp<code>gtk</code>
+					</p>
+					<p>
+						<img src="images/disabled_icons_desaturated.png" alt="Disablement option 'desaturated'" />
+						&nbsp<code>desaturated</code> (preview)
+					</p>
+				</td>
+			</tr>
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