[fix] Remove pulsar-broker-common dependency from pulsar-client

[nicoloboschi]

Motivation

#17198 added the pulsar-broker-common dependency to the pulsar-client module. This is very bad because in this way user applications will download the pulsar broker internals dependency and they may start using unsupported API.
Also this breaks the JDK 8 compatibility for the client. This looks like is no more covered by the CI and I will address it in another pull.

Modifications

• Moved BaseGenerateDocumentation to the pulsar-common module
• Moved source code compatibility to JDK8
• Replaced FieldContext usage with reflections because it's no more accessible
• Set the release flag to 8 for the packages-core module
• Added the enforcer to the pulsar-client-all module to verify binary compatibility to jdk8

• doc-not-needed

Fork test runs: nicoloboschi#17

[BewareMyPower]

LGTM. Could you open a match PR in your fork to verify it?

[lhotari]

I'd suggest applying https://www.mojohaus.org/extra-enforcer-rules/enforceBytecodeVersion.html to prevent future regressions. The Pulsar client modules must be JDK 8 only. This applies to pulsar-common too.

[nicoloboschi]

@lhotari I added the enforcer, it was a great suggestion.

Thanks to it, I found out that also pulsar-package-core is included in pulsar-admin-client dependency, since 2020. (I guess Pulsar 2.6). So we cannot remove the package without a breaking change. We could eventually move used classes to the pulsar-client-admin-api module. If a user inadvertly imported some internal classes from pulsar-package-core, they will get errors during the client upgrade. However I think it's fine to change it starting from 2.12.0

Since Pulsar 2.11 will be released using the maven release flag to 17, we absolutely need to apply my latest commit 82beb7b to branch-2.11 before cutting the release
EDIT: I just tried to create a JDK8 application that uses the Pulsar admin client, upgrading dependency to 2.11.0-SNAPSHOT (without this pull change) and I get the expected error

java.lang.UnsupportedClassVersionError: org/apache/pulsar/packages/management/core/common/PackageName has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 52.0
    at java.lang.ClassLoader.defineClass1 (Native Method)
    at java.lang.ClassLoader.defineClass (ClassLoader.java:757)
    at java.security.SecureClassLoader.defineClass (SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass (URLClassLoader.java:473)
    at java.net.URLClassLoader.access$100 (URLClassLoader.java:74)
    at java.net.URLClassLoader$1.run (URLClassLoader.java:369)
    at java.net.URLClassLoader$1.run (URLClassLoader.java:363)
    at java.security.AccessController.doPrivileged (Native Method)
    at java.net.URLClassLoader.findClass (URLClassLoader.java:362)
    at java.lang.ClassLoader.loadClass (ClassLoader.java:419)
    at java.lang.ClassLoader.loadClass (ClassLoader.java:352)
    at org.apache.pulsar.client.admin.internal.PackagesImpl.getMetadataAsync (PackagesImpl.java:69)
    at org.apache.pulsar.client.admin.internal.PackagesImpl.lambda$getMetadata$0 (PackagesImpl.java:64)
    at org.apache.pulsar.client.admin.internal.BaseResource.sync (BaseResource.java:292)
    at org.apache.pulsar.client.admin.internal.PackagesImpl.getMetadata (PackagesImpl.java:64)
    at com.nicoloboschi.MainClient.main (MainClient.java:26)

Main class:

public static void main(String[] args) throws Exception {
        @Cleanup
        final PulsarAdmin admin = PulsarAdmin.builder()
                .serviceHttpUrl("http://localhost:8080")
                .build();
        final PackageMetadata mypackage = admin.packages().getMetadata("mypackage");

    }

I opened a pull against 2.11 #17873

[lhotari]

LGTM

[nicoloboschi]

/pulsarbot rerun-failure-checks