Some Colors and Fonts entries already provide user facing descriptions

via ThemeElementCategory, while others do not.
This change uses the existing descriptions to display in the description
box and adds description for ones that doesn't have any entries to
ensure the description area is not left empty and that available
descriptions are consistently utilised.

The main change pertaining to this has been merged in
eclipse.platform.ui and eclipse.platform via
eclipse-platform/eclipse.platform.ui#3666 and
eclipse-platform/eclipse.platform#2453
respectively. One of the remaining part pertaining to the above PR's are
addressed via this change.

Author: elsazac

org.eclipse.jdt.ui/plugin.properties

@@ -155,6 +155,8 @@ ModuleInfoClassFileViewerName=Module-Info Class File Viewer
 javaEditorFontDefiniton.label= Java Editor Text Font
 javaEditorFontDefintion.description= The Java editor text font is used by Java editors.
 
+JavaTheme.description= Colors and fonts used in the Java editor, Javadoc and Java views.
+
 javaCompareFontDefiniton.label= Java compare text font
 javaCompareFontDefiniton.description= The Java compare text font is used by Java compare/merge tools.
 

org.eclipse.jdt.ui/plugin.xml

@@ -1190,9 +1190,14 @@
             class="org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitDocumentProvider"/>
    </extension>
 
-   <extension
-         point="org.eclipse.ui.themes">
-        <themeElementCategory label="%javaPresentation.label" id="org.eclipse.jdt.ui.presentation"/>
+   <extension point="org.eclipse.ui.themes">
+        <themeElementCategory 
+        	label="%javaPresentation.label" 
+        	id="org.eclipse.jdt.ui.presentation">
+         	<description>
+            	%JavaTheme.description
+         	</description>
+        </themeElementCategory>
       <fontDefinition
             label="%javaEditorFontDefiniton.label"
             defaultsTo="org.eclipse.jface.textfont"