Replace guava's with JDK streams

Reduce dependency on guava to avoid potential conflicts when multiple
versions of guava are in the classpath.

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/internal/gradle/checksums/WrapperValidator.java

@@ -31,6 +31,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -47,10 +48,6 @@
 import org.osgi.framework.Bundle;
 
 import com.google.common.base.Charsets;
-import com.google.common.base.Function;
-import com.google.common.base.Predicate;
-import com.google.common.collect.FluentIterable;
-import com.google.common.collect.ImmutableList;
 import com.google.common.io.CharStreams;
 import com.google.common.io.Closeables;
 import com.google.gson.Gson;
@@ -110,21 +107,10 @@ public ValidationResult checkWrapper(String baseDir) throws CoreException {
 					};
 					List<Map<String, String>> versions = gson.fromJson(json, typeToken.getType());
 					//@formatter:off
-					ImmutableList<String> urls = FluentIterable
-						.from(versions)
-						.filter(new Predicate<Map<String, String>>() {
-							@Override
-							public boolean apply(Map<String, String> input) {
-								return input.get(WRAPPER_CHECKSUM_URL) != null;
-							}
-						})
-						.transform(new Function<Map<String, String>, String>() {
-							@Override
-							public String apply(Map<String, String> input) {
-								return input.get(WRAPPER_CHECKSUM_URL);
-							}
-						})
-					.toList();
+					List<String> urls = versions.stream()
+						.map(input -> input.get(WRAPPER_CHECKSUM_URL))
+						.filter(Objects::nonNull)
+						.toList();
 					// @formatter:on
 					DownloadChecksumJob downloadJob = new DownloadChecksumJob();
 					int count = 0;