Fix Dokka links to Spring Framework and Servlet APIs

This commit fixes links from Spring Framework's Dokka HTML to Javadoc
for Spring Framework and Servlet APIs by explicitly configuring the
`element-list` page as the `package-list` in the Dokka Gradle plugin.

Closes gh-32797

(cherry picked from commit 7536980)

Author: sbrannen

Diff for: gradle/docs-dokka.gradle

@@ -6,6 +6,7 @@ tasks.findByName("dokkaHtmlPartial")?.configure {
 			classpath.from(sourceSets["main"].runtimeClasspath)
 			externalDocumentationLink {
 				url.set(new URL("https://docs.spring.io/spring-framework/docs/current/javadoc-api/"))
+				packageListUrl.set(new URL("https://docs.spring.io/spring-framework/docs/current/javadoc-api/element-list"))
 			}
 			externalDocumentationLink {
 				url.set(new URL("https://projectreactor.io/docs/core/release/api/"))
@@ -21,6 +22,7 @@ tasks.findByName("dokkaHtmlPartial")?.configure {
 			}
 			externalDocumentationLink {
 				url.set(new URL("https://javadoc.io/doc/jakarta.servlet/jakarta.servlet-api/latest/"))
+				packageListUrl.set(new URL("https://javadoc.io/doc/jakarta.servlet/jakarta.servlet-api/latest/element-list"))
 			}
 			externalDocumentationLink {
 				url.set(new URL("https://javadoc.io/static/io.rsocket/rsocket-core/1.1.1/"))