Prioritize Maven packages over the JDK when exporting monikers

Previously, when a Maven package re-defined a class from the JDK then
lsif-java would emit an export against the JDK instead of the Maven
package. This caused problems with navigation to the JDK on Sourcegraph
because there were multiple repositories that exported monikers against
the `jdk/8` packageInformation node. Now, only the JDK repo should
export monikers for the JDK repo.

Author: olafurpg

lsif-semanticdb/src/main/java/com/sourcegraph/lsif_semanticdb/PackageTable.java

@@ -36,10 +36,14 @@ public class PackageTable implements Function<Package, Integer> {
   public PackageTable(LsifSemanticdbOptions options, LsifWriter writer) throws IOException {
     this.writer = writer;
     this.javaVersion = new JavaVersion();
+    // NOTE: it's important that we index the JDK before maven packages. Some maven packages
+    // redefine classes from the JDK and we want those maven packages to take precedence over
+    // the JDK. The motivation to prioritize maven packages over the JDK is that we only want
+    // to exports monikers against the JDK when indexing the JDK repo.
+    indexJdk();
     for (MavenPackage pkg : options.packages) {
       indexPackage(pkg);
     }
-    indexJdk();
   }
 
   public void writeImportedSymbol(String symbol, int monikerId) {