Add Access-Control-Allow-Private-Network header to common library.

https://developer.chrome.com/blog/private-network-access-update

RELNOTES=`net`: Added `HttpHeaders` constant for `Access-Control-Allow-Private-Network`.
PiperOrigin-RevId: 426407160

Author: java-team-github-bot

android/guava/src/com/google/common/net/HttpHeaders.java

@@ -199,6 +199,14 @@ private ReferrerPolicyValues() {}
   public static final String ACCESS_CONTROL_ALLOW_METHODS = "Access-Control-Allow-Methods";
   /** The HTTP {@code Access-Control-Allow-Origin} header field name. */
   public static final String ACCESS_CONTROL_ALLOW_ORIGIN = "Access-Control-Allow-Origin";
+  /**
+   * The HTTP <a href="https://wicg.github.io/private-network-access/#headers">{@code
+   * Access-Control-Allow-Private-Network}</a> header field name.
+   *
+   * @since NEXT
+   */
+  public static final String ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK =
+      "Access-Control-Allow-Private-Network";
   /** The HTTP {@code Access-Control-Allow-Credentials} header field name. */
   public static final String ACCESS_CONTROL_ALLOW_CREDENTIALS = "Access-Control-Allow-Credentials";
   /** The HTTP {@code Access-Control-Expose-Headers} header field name. */

guava/src/com/google/common/net/HttpHeaders.java

@@ -199,6 +199,14 @@ private ReferrerPolicyValues() {}
   public static final String ACCESS_CONTROL_ALLOW_METHODS = "Access-Control-Allow-Methods";
   /** The HTTP {@code Access-Control-Allow-Origin} header field name. */
   public static final String ACCESS_CONTROL_ALLOW_ORIGIN = "Access-Control-Allow-Origin";
+  /**
+   * The HTTP <a href="https://wicg.github.io/private-network-access/#headers">{@code
+   * Access-Control-Allow-Private-Network}</a> header field name.
+   *
+   * @since NEXT
+   */
+  public static final String ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK =
+      "Access-Control-Allow-Private-Network";
   /** The HTTP {@code Access-Control-Allow-Credentials} header field name. */
   public static final String ACCESS_CONTROL_ALLOW_CREDENTIALS = "Access-Control-Allow-Credentials";
   /** The HTTP {@code Access-Control-Expose-Headers} header field name. */