SOLR-18289: Upgrade Gradle build to 9.6.0

[serhiy-bzhezytskyy]

https://issues.apache.org/jira/browse/SOLR-18289

Description

Upgrades Solr's build from Gradle 8.10 to 9.6.0 (the current stable Gradle release). Solr is currently a full major version behind; this brings the build onto Gradle 9.x. The Java baseline is unchanged (Java 21) — this is purely a build-tool upgrade.

For reference, Lucene already completed the same 8 -> 9 migration and is on 9.6.0, so the migration path is well-trodden. (As discussed on the dev@ thread, Solr's build is independent of Lucene's; the one place version alignment helps is the lucene-dev composite build, which uses includeBuild against a local Lucene checkout.)

Changes

Gradle 8 -> 9 API migrations:

• Wrapper + version catalog -> 9.6.0.
• archivesBaseName -> base { archivesName }; sourceCompatibility / targetCompatibility moved under the java { } extension.
• Project.exec / Project.javaexec are removed in Gradle 9 -> inject ExecOperations (the quietExec helper, ChangesToHtmlTask, CheckBrokenLinksTask, JavaCCTask).
• ProjectDependency.dependencyProject -> dep / project(dep.path).
• Archive/copy file modes -> dirPermissions / filePermissions / permissions { unix(...) }.
• RAT classpath resolved at configuration time (Gradle 9 forbids resolving configurations at execution time).
• jar-checks: drop the now-forbidden setCanBeConsumed(true) on a copied resolvable configuration.
• render-javadoc: findRenderTasksInDependencies() made non-private (Groovy 4 dispatch on decorated task instances).
• rat-sources: explicit import groovy.xml.XmlParser (Groovy 4).
• webapp: webAppDirName -> from("web").

Other:

• Dependency analysis: the ca.cutterslade.analyze plugin has no Gradle-9-compatible release; with Gradle dependency locking enabled (which Solr uses) it produces false-positive "unused dependency" failures across modules — see gradle-dependency-analyze#810. So this PR removes it — matching Lucene main, which carries no dependency-analysis plugin. Per the dev@ thread, adopting a Gradle-9-native replacement (e.g. the autonomousapps Dependency Analysis Gradle Plugin) is left as a separate follow-up so it doesn't block the build-tool upgrade.
• netty-tcnative: the catalog pinned netty = 4.2.15 but netty-tcnative = 2.0.75; the netty BOM forces 2.0.77 in one module, so two versions resolved. Aligned the pin to 2.0.77 and updated the license checksum files.
• The wrapper-bootstrap JDK upper bound is raised 23 -> 25 in a separate commit so it can be dropped easily if considered out of scope.

Lockfiles regenerated on Java 21.

Testing

Verified on Eclipse Temurin 21:

• ./gradlew check (compile + all lint/validation: RAT, jar-checks, forbidden-apis, spotless, javadoc, broken-links, ecj) passes.
• Per-module test suites pass. The full parallel ./gradlew test is intermittently flaky on a developer machine independent of this change (e.g. SolrProcessManagerTest spawns child JVMs and binds ports — a TOCTOU race; CollectionsAPISolrJTest ZK-watcher timing); the same failures reproduce on an unmodified main checkout and pass on rerun / in isolation.

AI assistance disclosure

Per Solr's AGENTS.md / how-to-contribute guidance: this change was prepared with the assistance of an AI coding agent and has been reviewed by me for correctness, scope, and alignment with Solr's build conventions.