Load the CC API with services loaders

This is a little odd (it's more complex for one!), but means we can
reuse the internal API interface in other classes, which is useful for
the data provider refactor I'm about to do.

This is much nicer in Java 17 :D (records, ServiceLoader.stream()),
but such is the perils of still targetting 1.16.

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

@@ -0,0 +1,20 @@
+package cc.tweaked.gradle
+
+import org.gradle.api.artifacts.dsl.DependencyHandler
+import org.gradle.api.tasks.JavaExec
+
+fun DependencyHandler.annotationProcessorEverywhere(dep: Any) {
+    add("compileOnly", dep)
+    add("annotationProcessor", dep)
+
+    add("testCompileOnly", dep)
+    add("testAnnotationProcessor", dep)
+}
+
+fun JavaExec.copyToFull(spec: JavaExec) {
+    copyTo(spec)
+    spec.classpath = classpath
+    spec.mainClass.set(mainClass)
+    spec.javaLauncher.set(javaLauncher)
+    spec.args = args
+}