Publish a javadoc jar with content again (#205)

The javadoc jar has been empty since 0.2.10: with source 17 the javadoc
plugin treats the project as modular (module-info.java in java9 and java17)
and finds no sources. Use ${java.version} like the compiler does, and fail
the build when javadoc fails; jackson-base turns that off. The inherited
Java 8 API link goes: javadoc on JDK 25 rejects its redirect.

Author: Sekator778

pom.xml

@@ -270,10 +270,13 @@
                     </execution>
                 </executions>
                 <configuration>
-                    <source>17</source>
+                    <source>${java.version}</source>
                     <doclint>none</doclint>
                     <detectJavaApiLink>false</detectJavaApiLink>
                     <failOnWarnings>false</failOnWarnings>
+                    <failOnError>true</failOnError>
+                    <!-- the inherited Java 8 API link redirects, and javadoc on JDK 25 fails on it -->
+                    <links combine.self="override"/>
                     <quiet>true</quiet>
                     <additionalOptions>
                         <additionalOption>-Xdoclint:none</additionalOption>