immutable Pair, better performant HttpBearerAuth, consistent code-style (#20743)

* make Pair immutable and in google-code-style

* apply google-code-style to JavaTimeFormatter (to make it consistent with most other auto-generated java)

* move upperCaseBearer to ctor (scheme is final and private; only needs to be fixed once); also replaced Optional with ternary (perf and cleaner code)

* apply google-code-style to Authentication to make it consistent with rest of auth code

* fresh samples

samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/Pair.java

@@ -15,43 +15,23 @@ package org.openapitools.client;
 
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
 public class Pair {
-    private String name = "";
-    private String value = "";
+  private final String name;
+  private final String value;
 
-    public Pair (String name, String value) {
-        setName(name);
-        setValue(value);
-    }
+  public Pair(String name, String value) {
+    this.name = isValidString(name) ? name : "";
+    this.value = isValidString(value) ? value : "";
+  }
 
-    private void setName(String name) {
-        if (!isValidString(name)) {
-            return;
-        }
+  public String getName() {
+    return this.name;
+  }
 
-        this.name = name;
-    }
+  public String getValue() {
+    return this.value;
+  }
 
-    private void setValue(String value) {
-        if (!isValidString(value)) {
-            return;
-        }
-
-        this.value = value;
-    }
-
-    public String getName() {
-        return this.name;
-    }
-
-    public String getValue() {
-        return this.value;
-    }
-
-    private boolean isValidString(String arg) {
-        if (arg == null) {
-            return false;
-        }
-
-        return true;
-    }
+  private static boolean isValidString(String arg) {
+    return arg != null;
+  }
 }