Replace Prototype.js with native JavaScript

[basil]

See JENKINS-70906. Jenkins core currently uses Prototype 1.7, released on November 15, 2010. The latest version is Prototype 1.7.3, released on September 22, 2015. When an attempt was made to upgrade to 1.7.3 in 2018 in JENKINS-49319, the change had to be reverted. Since this library has been unmaintained for the past 8 years, this PR removes any usages of it in favor of native JavaScript APIs. To test this, I instrumented the code with

diff --git a/src/test/java/hudson/plugins/copyartifact/monitor/LegacyJobConfigMigrationMonitorMigrationTest.java b/src/test/java/hudson/plugins/copyartifact/monitor/LegacyJobConfigMigrationMonitorMigrationTest.java
index 64b7e85..6726de2 100644
--- a/src/test/java/hudson/plugins/copyartifact/monitor/LegacyJobConfigMigrationMonitorMigrationTest.java
+++ b/src/test/java/hudson/plugins/copyartifact/monitor/LegacyJobConfigMigrationMonitorMigrationTest.java
@@ -57,6 +57,7 @@ import jenkins.branch.BranchProperty;
 import jenkins.branch.BranchSource;
 import jenkins.branch.DefaultBranchPropertyStrategy;
 import jenkins.branch.NoTriggerBranchProperty;
+import jenkins.model.Jenkins;
 import jenkins.plugins.git.GitSCMSource;
 import jenkins.plugins.git.GitSampleRepoRule;
 
@@ -91,6 +92,7 @@ public class LegacyJobConfigMigrationMonitorMigrationTest {
         // anonymous cannot read jobs.
         j.jenkins.setSecurityRealm(j.createDummySecurityRealm());
         MockAuthorizationStrategy authStrategy = new MockAuthorizationStrategy();
+        authStrategy.grant(Jenkins.ADMINISTER).everywhere().to("admin");
         j.jenkins.setAuthorizationStrategy(authStrategy);
     }
 
@@ -111,6 +113,7 @@ public class LegacyJobConfigMigrationMonitorMigrationTest {
         );
 
         j.assertBuildStatusSuccess(dst.scheduleBuild2(0));
+        j.interactiveBreak();
 
         CopyArtifactConfiguration.get().setMode(CopyArtifactCompatibilityMode.PRODUCTION);
 

and then ran mvn clean verify -Djenkins.version=2.405-SNAPSHOT -Dtest=hudson.plugins.copyartifact.monitor.LegacyJobConfigMigrationMonitorMigrationTest#migrate_freestyle_to_freestyle. I visited http://localhost:45437/jenkins/manage/administrativeMonitor/copyArtifactLegacyJobConfigMigration/manage and set breakpoints on both fetch functions. I was able to hit both breakpoints successfully.

[allancth]

I would like to help testing the changes but I do not know where to start. Where/when are these Javascript functions called?

I am testing interactively with mvn hpi:run.

[basil]

This pull request has already been tested, and the pull request description describes the testing that was done.