8209358: Broken links in API docs for css page, fxml page, and all image files

Reviewed-by: prr

Author: kcr

build.gradle

@@ -4423,7 +4423,10 @@ task javadoc(type: Javadoc, dependsOn: createMSPfile) {
         ]);
 
     doLast {
+        // FIXME: remove JDK 10 logic once minimum JDK is bumped to 11
+        def isBootJdk10 = jdkVersion.startsWith("10")
         projectsToDocument.each { p ->
+            def destDir = isBootJdk10 ? "$buildDir/javadoc" : "$buildDir/javadoc/${p.ext.moduleName}"
             copy {
                 from("$p.projectDir/src/main/docs") {
                     include "**/*.html"
@@ -4435,7 +4438,7 @@ task javadoc(type: Javadoc, dependsOn: createMSPfile) {
                     exclude "**/*.html"
                 }
 
-                into "$buildDir/javadoc"
+                into destDir
             }
         }
     }