Incorporate Equinox project feature changes (#8)

The Equinox projects will stop creating the feature
org.eclipse.equinox.serverside.sdk that is used to provide some p2
plugins to our RAP Tools build. Replace this feature with
org.eclipse.equinox.server.p2 that provides the missing bundles.

See eclipse-equinox/equinox.bundles#43

releng/org.eclipse.rap.tools.build/target.definition/org.eclipse.rap.tools.target.definition.target

@@ -20,7 +20,7 @@
             <unit id="org.eclipse.equinox.compendium.sdk.feature.group" version="3.22.300.v20220426-1329"/>
             <unit id="org.eclipse.equinox.core.feature.feature.group" version="1.13.600.v20220427-2211"/>
             <unit id="org.eclipse.equinox.core.sdk.feature.group" version="3.23.400.v20220428-0703"/>
-            <unit id="org.eclipse.equinox.serverside.sdk.feature.group" version="3.23.400.v20220428-0821"/>
+            <unit id="org.eclipse.equinox.server.p2.feature.group" version="1.12.500.v20220426-1329"/>
             <unit id="org.eclipse.jdt.feature.group" version="3.18.1200.v20220428-1800"/>
             <unit id="org.eclipse.jdt.source.feature.group" version="3.18.1200.v20220428-1800"/>
             <unit id="org.eclipse.pde.feature.group" version="3.14.1200.v20220428-1800"/>