Drop Java 8 source compatibility; it's unnecessary when class files are compiled for Java 11.

Author: AlexeyKuznetsov-DD

dd-java-agent/agent-iast/build.gradle

@@ -12,7 +12,7 @@ apply from: "$rootDir/gradle/java.gradle"
 apply from: "$rootDir/gradle/version.gradle"
 
 tasks.withType(AbstractCompile).configureEach {
-  configureCompiler(it, 11, JavaVersion.VERSION_1_8, "Ensure no APIs beyond JDK8 are used")
+  configureCompiler(it, 11)
 }
 
 // First version with Mac M1 support

dd-java-agent/agent-iast/src/main/java/com/datadog/iast/util/StringUtils.java

@@ -93,7 +93,7 @@ public static String replaceAndTaint(
       String finalReplacement = Matcher.quoteReplacement(replacement);
 
       boolean canAddRange = true;
-      StringBuffer sb = new StringBuffer();
+      StringBuilder sb = new StringBuilder();
       do {
         int start = matcher.start();
         int end = matcher.end();