Support Maven <exclusions> syntax within target <dependency> elements

[vogella]

Closes #286

The m2-pde target location now accepts the standard Maven <exclusions>/<exclusion> syntax inside each <dependency> element, in addition to the existing location-level <exclude> elements.

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>5.9.3</version>
    <exclusions>
        <exclusion>
            <groupId>org.apiguardian</groupId>
            <artifactId>apiguardian-api</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Exclusions are per-dependency (not global) and are applied during transitive dependency collection via MavenDependencyCollector, consistent with standard Maven semantics. The * wildcard is supported for groupId and artifactId. The format round-trips correctly through serialize()/parse.

[github-actions]

Test Results

  336 files  ± 0    336 suites  ±0   1h 3m 24s ⏱️ - 7m 6s
  718 tests + 4    699 ✅ + 3  16 💤 ±0  1 ❌ ±0  2 🔥 +1 
2 154 runs  +12  2 103 ✅ +11  48 💤 ±0  1 ❌ ±0  2 🔥 +1 

For more details on these failures and errors, see this check.

Results for commit 21c6ca4. ± Comparison against base commit 98b66b5.

[laeubi]

I'm missing UI integration for this feature through the target location editor and the dependency tree.

Additionally we already have a way to exclude dependencies, so one would expect this code path to be enhanced instead of adding a complete new codepath.