Improve our version tooling

- Add a check to ensure declared dependencies in the :core project, and
   those inherited from Minecraft are the same.
 - Compute the next Cobalt version, rather than specifying it manually.
 - Add the gradle versions plugin (and version catalog update), and
   update some versions.

buildSrc/src/main/kotlin/cc/tweaked/gradle/DependencyCheck.kt

@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: 2023 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package cc.tweaked.gradle
+
+import org.gradle.api.DefaultTask
+import org.gradle.api.GradleException
+import org.gradle.api.artifacts.Configuration
+import org.gradle.api.artifacts.component.ModuleComponentIdentifier
+import org.gradle.api.artifacts.component.ModuleComponentSelector
+import org.gradle.api.artifacts.component.ProjectComponentIdentifier
+import org.gradle.api.artifacts.result.DependencyResult
+import org.gradle.api.artifacts.result.ResolvedDependencyResult
+import org.gradle.api.provider.ListProperty
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.TaskAction
+import org.gradle.language.base.plugins.LifecycleBasePlugin
+
+abstract class DependencyCheck : DefaultTask() {
+    @get:Input
+    abstract val configuration: ListProperty<Configuration>
+
+    init {
+        description = "Check :core's dependencies are consistent with Minecraft's."
+        group = LifecycleBasePlugin.VERIFICATION_GROUP
+    }
+
+    @TaskAction
+    fun run() {
+        var ok = true
+        for (configuration in configuration.get()) {
+            configuration.incoming.resolutionResult.allDependencies {
+                if (!check(this@allDependencies)) ok = false
+            }
+        }
+
+        if (!ok) {
+            throw GradleException("Mismatched versions in Minecraft dependencies. gradle/libs.versions.toml may need updating.")
+        }
+    }
+
+    private fun check(dependency: DependencyResult): Boolean {
+        if (dependency !is ResolvedDependencyResult) {
+            logger.warn("Found unexpected dependency result {}", dependency)
+            return false
+        }
+
+        // Skip dependencies on non-modules.
+        val requested = dependency.requested
+        if (requested !is ModuleComponentSelector) return true
+
+        // If this dependency is specified within some project (so is non-transitive), or is pulled in via Minecraft,
+        // then check for consistency.
+        // It would be nice to be smarter about transitive dependencies, but avoiding false positives is hard.
+        val from = dependency.from.id
+        if (
+            from is ProjectComponentIdentifier ||
+            from is ModuleComponentIdentifier && (from.group == "net.minecraft" || from.group == "io.netty")
+        ) {
+            // If the version is different between the requested and selected version, report an error.
+            val selected = dependency.selected.moduleVersion!!.version
+            if (requested.version != selected) {
+                logger.error("Requested dependency {} (via {}) but got version {}", requested, from, selected)
+                return false
+            }
+
+            return true
+        }
+        return true
+    }
+}