Require JDK 17 rather than JDK 11 (#603)

By raising this baseline the project can now use Java 17 language features such
as text blocks, switch expressions and `instanceof` pattern matching. The code
has been updated to make use of these constructs.

Note that the project can still be used by builds that target an older version
of Java, as long as those builds are executed using JDK 17+.

refaster-test-support/pom.xml

@@ -106,9 +106,6 @@
                                 <version>${project.version}</version>
                             </path>
                         </annotationProcessorPaths>
-                        <compilerArgs combine.children="append">
-                            <arg>-Xplugin:RefasterRuleCompiler</arg>
-                        </compilerArgs>
                     </configuration>
                 </plugin>
             </plugins>

refaster-test-support/src/main/java/tech/picnic/errorprone/refaster/test/RefasterRuleCollection.java

@@ -154,8 +154,8 @@ public final class RefasterRuleCollection extends BugChecker implements Compilat
     String expectedClassName = ruleCollectionUnderTest + "Test";
 
     for (Tree typeDeclaration : tree.getTypeDecls()) {
-      if (typeDeclaration instanceof ClassTree) {
-        if (!((ClassTree) typeDeclaration).getSimpleName().contentEquals(expectedClassName)) {
+      if (typeDeclaration instanceof ClassTree classTree) {
+        if (!classTree.getSimpleName().contentEquals(expectedClassName)) {
           state.reportMatch(
               describeMatch(
                   typeDeclaration,
@@ -276,9 +276,10 @@ public final class RefasterRuleCollection extends BugChecker implements Compilat
             unexpectedMatchesByLineNumber.entries().stream()
                 .map(
                     e ->
-                        String.format(
-                            "Rule `%s` matches on line %s, while it should match in a method named `test%s`.",
-                            e.getValue(), e.getKey(), e.getValue()))
+                        """
+                        Rule `%s` matches on line %s, while it should match in a method named \
+                        `test%s`."""
+                            .formatted(e.getValue(), e.getKey(), e.getValue()))
                 .collect(toImmutableSet()),
             state);
       }