(Sonar) Fixed finding: "Utility classes should not have public constructors" (#395)

## Remediation

This change fixes "Utility classes should not have public constructors"
(id = [java:S1118](https://rules.sonarsource.com/java/RSPEC-1118/))
identified by Sonar.

## Details

This change adds private constructors to utility classes. Utility
classes are only meant to be accessed statically. Since they're not
meant to be instantiated, we can use the Java's code visibility
protections to hide the constructor and prevent unintended or malicious
access.

Our changes look something like this:

```diff
   public class Utils {
+    private Utils() {}
     ...
```

<details>
  <summary>More reading</summary>

*
[https://rules.sonarsource.com/java/RSPEC-1118/](https://rules.sonarsource.com/java/RSPEC-1118/)
</details>

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core-codemods/src/main/java/io/codemodder/codemods/ResourceLeakFixer.java

@@ -31,6 +31,8 @@
  */
 final class ResourceLeakFixer {
 
+  private ResourceLeakFixer() {}
+
   private static final Logger LOG = LoggerFactory.getLogger(ResourceLeakFixer.class);
 
   private static final String rootPrefix = "resource";

framework/codemodder-base/src/main/java/io/codemodder/Runner.java

@@ -7,6 +7,8 @@
 /** Provides an entrypoint for CLIs built with the codemodder framework. */
 public final class Runner {
 
+  private Runner() {}
+
   /**
    * Runs the codemods with a set of customized streams.
    *

framework/codemodder-base/src/main/java/io/codemodder/ast/ASTTransforms.java

@@ -30,6 +30,8 @@
 
 public final class ASTTransforms {
   /** Add an import in alphabetical order. */
+  private ASTTransforms() {}
+
   public static void addImportIfMissing(final CompilationUnit cu, final String className) {
     final NodeList<ImportDeclaration> imports = cu.getImports();
     final ImportDeclaration newImport = new ImportDeclaration(className, false, false);

framework/codemodder-base/src/main/java/io/codemodder/ast/ASTs.java

@@ -31,6 +31,8 @@
 /** A static library for querying and returning patterns over AST nodes. */
 public final class ASTs {
 
+  private ASTs() {}
+
   /**
    * Test for this pattern: {@link AssignExpr} -> {@link Expression} ({@code expr}), where
    * ({@code expr}) is the right hand side expression of the assignment.

framework/codemodder-base/src/main/java/io/codemodder/ast/NameResolver.java

@@ -10,6 +10,8 @@
 /** Find sources of names in JavaParser ASTs. */
 final class NameResolver {
 
+  private NameResolver() {}
+
   private static Optional<Node> isLocalNameSource(final Node n, final String name) {
     final Optional<Node> maybe =
         ASTs.isExpressionStmtDeclarationOf(n, name).map(Triplet::getValue2);

framework/codemodder-testutils-llm/src/main/java/io/codemodder/testutils/llm/CodemodderOpenAIKeys.java

@@ -7,6 +7,8 @@
 @SuppressWarnings("unused")
 public final class CodemodderOpenAIKeys {
 
+  private CodemodderOpenAIKeys() {}
+
   /**
    * Return true if and only if we have a non-empty {@code CODEMODDER_OPENAI_API_KEY} environment
    * variable.