Migrate buildSrc to composite build (#4090)

This will help reduce build times when changes are made to the precompiled
script plugins used in the build. This is because a change in buildSrc
causes the whole project to become out-of-date [0]. Using an included build
instead works around this problem.

[0] https://docs.gradle.org/7.2/userguide/organizing_gradle_projects.html#sec:build_sources

detekt-rules-complexity/build.gradle.kts

@@ -1,5 +1,5 @@
 plugins {
-    module
+    id("module")
 }
 
 dependencies {