Drop support for side-files

[jglick]

While waiting a long time for a config page to load in a newly started controller, I decided to take a thread dump, and noticed this:

"Handling GET /mc/manage/configureClouds/ from … : Jetty (winstone)-… KubernetesCloud/DescriptorImpl/config.jelly PodTemplate/config.jelly" Id=… Group=main RUNNABLE
	at java.base@11.0.20/sun.nio.fs.UnixNativeDispatcher.lstat(UnixNativeDispatcher.java:334)
	at java.base@11.0.20/sun.nio.fs.UnixFileAttributes.get(UnixFileAttributes.java:72)
	at java.base@11.0.20/sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes(UnixFileAttributeViews.java:52)
	at java.base@11.0.20/sun.nio.fs.UnixFileSystemProvider.readAttributes(UnixFileSystemProvider.java:149)
	at java.base@11.0.20/sun.nio.fs.LinuxFileSystemProvider.readAttributes(LinuxFileSystemProvider.java:99)
	at java.base@11.0.20/java.nio.file.Files.readAttributes(Files.java:1764)
	at java.base@11.0.20/java.nio.file.Files.isSymbolicLink(Files.java:2190)
	at org.eclipse.jetty.util.resource.PathResource.checkAliasPath(PathResource.java:98)
	at org.eclipse.jetty.util.resource.PathResource.<init>(PathResource.java:262)
	at org.eclipse.jetty.util.resource.PathResource.addPath(PathResource.java:367)
	at org.eclipse.jetty.server.handler.ContextHandler.getResource(ContextHandler.java:1947)
	at org.eclipse.jetty.webapp.WebAppContext.getResource(WebAppContext.java:410)
	at org.eclipse.jetty.webapp.WebAppContext$Context.getResource(WebAppContext.java:1444)
	at org.kohsuke.stapler.IndexHtmlDispatcher.make(IndexHtmlDispatcher.java:44)
	at org.kohsuke.stapler.MetaClass.buildDispatchers(MetaClass.java:153)
	at org.kohsuke.stapler.MetaClass.<init>(MetaClass.java:99)
	at org.kohsuke.stapler.WebApp$1.computeValue(WebApp.java:230)
	at org.kohsuke.stapler.WebApp$1.computeValue(WebApp.java:227)
	at java.base@11.0.20/java.lang.ClassValue.getFromHashMap(ClassValue.java:228)
	at java.base@11.0.20/java.lang.ClassValue.getFromBackup(ClassValue.java:210)
	at java.base@11.0.20/java.lang.ClassValue.get(ClassValue.java:116)
	at org.kohsuke.stapler.WebApp.getMetaClass(WebApp.java:246)
	at org.kohsuke.stapler.jelly.groovy.GroovyFacet.createRequestDispatcher(GroovyFacet.java:74)
	at org.kohsuke.stapler.RequestImpl.getView(RequestImpl.java:307)
	at org.kohsuke.stapler.RequestImpl.getView(RequestImpl.java:302)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:776)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:757)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:746)
	at …

Something spending time crawling the filesystem (not the jenkins.war) looking for something, but what?

stapler/core/src/main/java/org/kohsuke/stapler/IndexHtmlDispatcher.java

Line 10 in eca9c5f

* Serve {@code index.html} from {@code WEB-INF/side-files} if that exists.

but I have never heard of such a thing. History does not help much other than 95f7089 (#102)

Since this feature is rarely used…

In fact it seems this feature is never used at all. (Checked @cloudbees too.) Since we expect Stapler to only be used by Jenkins these days, we could simplify code and apparently speed up view initialization by dropping this feature.