Cross-project property lookups are incompatible with Gradle isolated projects

[Gradle isolated projects](https://docs.gradle.org/current/userguide/isolated_projects.html#sec:migration_path) restrict how one (sub)project can access mutable state in another (sub)project. Version 4.4.1 of the `com.diffplug.eclipse.mavencentral` plugin violates these restrictions. Attempting to use this plugin [with isolated projects enabled](https://docs.gradle.org/current/userguide/isolated_projects.html#sec:enable) results in errors like the following:

```terminaloutput
- Plugin 'com.diffplug.eclipse.mavencentral': Project ':xxx:yyy:zzz' cannot dynamically look up a property in the parent project ':xxx:yyy'
```

Using a stack trace for additional context reveals that the problematic code is at `GoomphCacheLocations.java:56` in `com.diffplug.gradle. GoomphCacheLocations. initFromProject(Project)`:

https://github.com/diffplug/goomph/blob/7e7e41cd68c100ff1e6efdc8010bf8e60b7500a7/src/main/java/com/diffplug/gradle/GoomphCacheLocations.java#L56

See also related discussion in gradle/gradle#36998. Note especially [this comment](https://github.com/gradle/gradle/issues/36998#issuecomment-4617263322) near the very end that "We are getting rid of the `Project.getProperties()` method."

Start with src/main/java/com/diffplug/gradle/GoomphCacheLocations.java at line 56 in GoomphCacheLocations.initFromProject(Project), then reproduce the failure with Gradle isolated projects enabled. Read the linked Gradle issue and its migration guidance, and verify the plugin no longer triggers the cross-project dynamic property lookup error.

Scritto dal modello di indicizzazione a partire dal testo della issue.