Issue #5492 - Adding java.features.* start properties

+ Simplifying alpn start modules in the process.
  (from 11 to 3)

Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>

jetty-alpn/jetty-alpn-server/src/main/config/modules/alpn.mod

@@ -5,7 +5,7 @@ Enables the ALPN (Application Layer Protocol Negotiation) TLS extension.
 
 [depend]
 ssl
-alpn-impl
+alpn-impl/alpn-available-${java.feature.alpn}
 
 [lib]
 lib/jetty-alpn-client-${jetty.version}.jar

jetty-start/src/main/java/org/eclipse/jetty/start/StartArgs.java

@@ -1505,6 +1505,12 @@ public void setProperty(String key, String value, String source)
             {
                 JavaVersion ver = JavaVersion.parse(value);
                 properties.setProperty("java.version.platform", Integer.toString(ver.getPlatform()), source);
+
+                // features built into java.
+                properties.setProperty("java.feature.alpn", Boolean.toString(ver.getPlatform() >= 9), source);
+                properties.setProperty("java.feature.jpms", Boolean.toString(ver.getPlatform() >= 9), source);
+                properties.setProperty("java.feature.loom", Boolean.toString(ver.getPlatform() >= 16), source);
+
                 // @deprecated - below will be removed in Jetty 10.x
                 properties.setProperty("java.version.major", Integer.toString(ver.getMajor()), "Deprecated");
                 properties.setProperty("java.version.minor", Integer.toString(ver.getMinor()), "Deprecated");