fix: restore Log4j2Plugins.dat in apm-toolkit-log4j-2.x (#825)

### Problem

Since **9.5.0**, the released `apm-toolkit-log4j-2.x` jar no longer contains the Log4j2 plugin descriptor:

```
META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat
```

Without that descriptor Log4j2 cannot discover `TraceIdConverter`, so `%traceId` and `%sw_ctx` in a `PatternLayout` silently break — they are greedily matched as the built-in `%t` (thread name) followed by literal text.

Verified against Maven Central:

| Version | `Log4j2Plugins.dat` |
|---------|---------------------|
| 9.0.0 – 9.4.0 | present |
| 9.5.0 – 9.7.0 | **missing** |

### Root Cause

9.5.0 added an `annotationProcessorPaths` block to `maven-compiler-plugin` in the root `pom.xml`, listing only Lombok. Once `annotationProcessorPaths` is declared explicitly, javac stops discovering annotation processors from the compile classpath. The `log4j-core` jar is declared as `provided` in this module, and Log4j2's `PluginProcessor` — previously picked up from that classpath — is what generates `Log4j2Plugins.dat`. With the processor list narrowed to Lombok only, `PluginProcessor` never runs and the descriptor is silently dropped.

### Fix

Declare the compiler plugin in this module with `annotationProcessorPaths` containing both Lombok (preserving parent behaviour) and `log4j-core` (restoring the `PluginProcessor`).