[7.0] Intentionally support Isolated Projects

[lolifamily]

With #992 and #991 done, the remaining Gradle isolation feature FG7 doesn't support is Isolated Projects, which parallelizes the configuration phase and requires that a project never reach into another project's model.

FG7 has exactly one violation. Gradle 9.6.1, -Dorg.gradle.unsafe.isolated-projects=true:

Project ':forge' cannot access 'Project.layout' functionality on another project ':'
  plugin class 'net.minecraftforge.gradle.internal.ForgeGradlePlugin'

It comes from the two plugin.rootProjectDirectory() calls in MinecraftExtensionImpl, which place the Mavenizer repo and the per-dependency JSONs under the root project's directory. ProjectLayout.getSettingsDirectory() resolves to the same location without going through another Project, so this may be a drop-in swap — and it overlaps with #1057, which wants that location configurable anyway.

[PaintNinja]

Isolated Projects is no longer experimental as of Gradle 9.7 and has new properties for enabling and troubleshooting it: https://docs.gradle.org/9.7.0/release-notes.html#isolated-projects

FG7 only having a single violation with a simple find and replace solution sounds promising, thanks.

[LexManos]

I am unsure how to fully test the isolated projects, but if its just a simple change it may be worth doing.
The root of this particular issue seems to be GradleUtils

So would need to be fixed there.

The main problem in FG tho, is going to be the run configs

ForgeGradle/src/main/java/net/minecraftforge/gradle/internal/SlimeLauncherEclipseConfiguration.java

Lines 466 to 470 in 8ae1fa8

	private static String getProjectEclipseName(Project project) {
	var eclipse = project.getExtensions().findByType(EclipseModel.class);
	var name = eclipse == null ? null : eclipse.getProject().getName();
	return name != null ? name : project.getName();
	}

We need a way to access the eclipse project name of other projects. I wrote that code mimicking what the official plugins do, and wouldn't doubt (as is gradle's history) that official plugins arnt compatible with their own features.

FG has two usages of plugin.rootProjectDirectory
The Mavenizer outputJson, honestly this could just be shoved in the per-project cache and probably be fine.

ForgeGradle/src/main/java/net/minecraftforge/gradle/internal/MinecraftExtensionImpl.java

Line 414 in 8ae1fa8

var outputJson = this.plugin.rootProjectDirectory().file(".gradle/mavenizer/dependencies/" + name + ".json").get().getAsFile();

The Mavenizer global output:
Which in theory should be fine to default to settings directory, and I think #1057 is resolved by virtue of DirectoryProperty getMavenizerOutput() being accessible. Should be able to do fg.mavenizerOutput = file('.gradle/mavenizer/repo/') per-project to isolate them.

ForgeGradle/src/main/java/net/minecraftforge/gradle/internal/MinecraftExtensionImpl.java

Line 97 in 8ae1fa8

this.mavenizerOutput.convention(plugin.rootProjectDirectory().dir(".gradle/mavenizer/repo").map(this.problems.ensureFileLocation()));

So ya, I think the proper fix is in GradleUtils, changing that to settings directory.