Configure JDK 24 toolchain for aggregated Javadoc

Changes made in conjunction with spring-projects#27497 now require that we generate
Javadoc with JDK 18 or higher in order to make use of the
"--link-modularity-mismatch" flag for the javadoc executable.

This commit sets the toolchain for the javadoc task in the
framework-api module to use JDK 24 for generating Javadoc.

The common javadoc task used by all spring-* modules will be addressed
in a separate commit.

See spring-projectsgh-27497
See spring-projectsgh-34774

Author: sbrannen

framework-api/framework-api.gradle

@@ -20,6 +20,10 @@ dependencies {
 }
 
 javadoc {
+	javadocTool.set(javaToolchains.javadocToolFor({
+		languageVersion = JavaLanguageVersion.of(24)
+	}))
+
 	title = "${rootProject.description} ${version} API"
 	options {
 		encoding = "UTF-8"